Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$249.62	11.791%	$279.0527	$279.05	$279.05	$279.10
Purchase #2	$203.75	4.842%	$213.6156	$213.62	$213.60	$213.60
Purchase #3	$226.80	6.810%	$242.2451	$242.25	$242.25	$242.20
Purchase #4	$96.93	13.199%	$109.7238	$109.72	$109.70	$109.70
Purchase #5	$226.73	9.847%	$249.0561	$249.06	$249.05	$249.10
Purchase #6	$172.61	13.853%	$196.5217	$196.52	$196.50	$196.50
Purchase #7	$152.25	6.467%	$162.096	$162.10	$162.10	$162.10
7 purchase totals =	$1,328.69		$1,452.3110	$1,452.32	$1,452.25	$1,452.30