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	$11.69	5.523%	$12.3356	$12.34	$12.35	$12.30
Purchase #2	$44.85	12.535%	$50.4719	$50.47	$50.45	$50.50
Purchase #3	$138.41	5.709%	$146.3118	$146.31	$146.30	$146.30
Purchase #4	$20.61	8.157%	$22.2912	$22.29	$22.30	$22.30
Purchase #5	$162.71	4.824%	$170.5591	$170.56	$170.55	$170.60
Purchase #6	$124.43	12.399%	$139.8581	$139.86	$139.85	$139.90
Purchase #7	$31.31	7.104%	$33.5343	$33.53	$33.55	$33.50
7 purchase totals =	$534.01		$575.3620	$575.36	$575.35	$575.40