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	$130.96	12.334%	$147.1126	$147.11	$147.10	$147.10
Purchase #2	$247.74	12.818%	$279.4953	$279.50	$279.50	$279.50
Purchase #3	$132.37	10.548%	$146.3324	$146.33	$146.35	$146.30
Purchase #4	$158.69	8.696%	$172.4897	$172.49	$172.50	$172.50
Purchase #5	$69.79	9.148%	$76.1744	$76.17	$76.15	$76.20
Purchase #6	$239.80	7.758%	$258.4037	$258.40	$258.40	$258.40
Purchase #7	$71.51	12.699%	$80.5911	$80.59	$80.60	$80.60
7 purchase totals =	$1,050.86		$1,160.5992	$1,160.59	$1,160.60	$1,160.60