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	$10.58	12.607%	$11.9138	$11.91	$11.90	$11.90
Purchase #2	$36.82	6.581%	$39.2431	$39.24	$39.25	$39.20
Purchase #3	$57.28	5.657%	$60.5203	$60.52	$60.50	$60.50
Purchase #4	$135.41	11.150%	$150.5082	$150.51	$150.50	$150.50
Purchase #5	$203.59	10.294%	$224.5476	$224.55	$224.55	$224.50
Purchase #6	$213.35	4.258%	$222.4344	$222.43	$222.45	$222.40
Purchase #7	$106.61	9.871%	$117.1335	$117.13	$117.15	$117.10
7 purchase totals =	$763.64		$826.3009	$826.29	$826.30	$826.10