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	$180.50	11.830%	$201.8532	$201.85	$201.85	$201.90
Purchase #2	$158.47	5.238%	$166.7707	$166.77	$166.75	$166.80
Purchase #3	$78.69	3.856%	$81.7243	$81.72	$81.70	$81.70
Purchase #4	$83.83	7.698%	$90.2832	$90.28	$90.30	$90.30
Purchase #5	$162.98	6.839%	$174.1262	$174.13	$174.15	$174.10
Purchase #6	$84.62	13.495%	$96.0395	$96.04	$96.05	$96.00
Purchase #7	$89.74	11.288%	$99.8699	$99.87	$99.85	$99.90
7 purchase totals =	$838.83		$910.6670	$910.66	$910.65	$910.70