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	$123.76	13.440%	$140.3933	$140.39	$140.40	$140.40
Purchase #2	$127.58	10.112%	$140.4809	$140.48	$140.50	$140.50
Purchase #3	$204.37	8.781%	$222.3157	$222.32	$222.30	$222.30
Purchase #4	$84.75	7.299%	$90.9359	$90.94	$90.95	$90.90
Purchase #5	$183.73	6.823%	$196.2659	$196.27	$196.25	$196.30
Purchase #6	$241.95	13.785%	$275.3028	$275.30	$275.30	$275.30
Purchase #7	$217.69	3.463%	$225.2286	$225.23	$225.25	$225.20
7 purchase totals =	$1,183.83		$1,290.9231	$1,290.93	$1,290.95	$1,290.90