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	$229.58	9.170%	$250.6325	$250.63	$250.65	$250.60
Purchase #2	$50.54	11.733%	$56.4699	$56.47	$56.45	$56.50
Purchase #3	$101.94	8.387%	$110.4897	$110.49	$110.50	$110.50
Purchase #4	$232.54	11.349%	$258.931	$258.93	$258.95	$258.90
Purchase #5	$147.74	3.282%	$152.5888	$152.59	$152.60	$152.60
Purchase #6	$25.69	12.108%	$28.8005	$28.80	$28.80	$28.80
Purchase #7	$11.69	5.561%	$12.3401	$12.34	$12.35	$12.30
7 purchase totals =	$799.72		$870.2525	$870.25	$870.30	$870.20