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	$22.71	8.505%	$24.6415	$24.64	$24.65	$24.60
Purchase #2	$161.82	3.379%	$167.2879	$167.29	$167.30	$167.30
Purchase #3	$247.96	6.676%	$264.5138	$264.51	$264.50	$264.50
Purchase #4	$87.60	5.200%	$92.1552	$92.16	$92.15	$92.20
Purchase #5	$20.33	10.725%	$22.5104	$22.51	$22.50	$22.50
Purchase #6	$52.46	3.865%	$54.4876	$54.49	$54.50	$54.50
Purchase #7	$141.72	4.389%	$147.9401	$147.94	$147.95	$147.90
7 purchase totals =	$734.60		$773.5365	$773.54	$773.55	$773.50