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	$75.98	12.594%	$85.5489	$85.55	$85.55	$85.50
Purchase #2	$214.93	7.416%	$230.8692	$230.87	$230.85	$230.90
Purchase #3	$37.45	4.444%	$39.1143	$39.11	$39.10	$39.10
Purchase #4	$131.96	11.348%	$146.9348	$146.93	$146.95	$146.90
Purchase #5	$33.36	3.275%	$34.4525	$34.45	$34.45	$34.50
Purchase #6	$59.87	4.434%	$62.5246	$62.52	$62.50	$62.50
Purchase #7	$148.55	13.444%	$168.5211	$168.52	$168.50	$168.50
7 purchase totals =	$702.10		$767.9654	$767.95	$767.90	$767.90