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	$9.37	12.122%	$10.5058	$10.51	$10.50	$10.50
Purchase #2	$68.91	3.548%	$71.3549	$71.35	$71.35	$71.40
Purchase #3	$19.61	13.344%	$22.2268	$22.23	$22.25	$22.20
Purchase #4	$189.73	11.694%	$211.917	$211.92	$211.90	$211.90
Purchase #5	$26.83	6.146%	$28.479	$28.48	$28.50	$28.50
Purchase #6	$142.27	11.258%	$158.2868	$158.29	$158.30	$158.30
Purchase #7	$54.33	4.871%	$56.9764	$56.98	$57.00	$57.00
7 purchase totals =	$511.05		$559.7467	$559.76	$559.80	$559.80