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	$100.93	12.224%	$113.2677	$113.27	$113.25	$113.30
Purchase #2	$68.41	12.255%	$76.7936	$76.79	$76.80	$76.80
Purchase #3	$141.32	6.251%	$150.1539	$150.15	$150.15	$150.20
Purchase #4	$154.69	7.282%	$165.9545	$165.95	$165.95	$166.00
Purchase #5	$39.63	5.862%	$41.9531	$41.95	$41.95	$42.00
Purchase #6	$54.37	13.131%	$61.5093	$61.51	$61.50	$61.50
Purchase #7	$58.98	11.634%	$65.8417	$65.84	$65.85	$65.80
7 purchase totals =	$618.33		$675.4738	$675.46	$675.45	$675.60