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	$85.83	5.391%	$90.4571	$90.46	$90.45	$90.50
Purchase #2	$65.34	3.657%	$67.7295	$67.73	$67.75	$67.70
Purchase #3	$139.47	9.419%	$152.6067	$152.61	$152.60	$152.60
Purchase #4	$30.69	4.761%	$32.1512	$32.15	$32.15	$32.20
Purchase #5	$155.85	5.278%	$164.0758	$164.08	$164.10	$164.10
Purchase #6	$231.97	10.634%	$256.6377	$256.64	$256.65	$256.60
Purchase #7	$90.55	9.272%	$98.9458	$98.95	$98.95	$98.90
7 purchase totals =	$799.70		$862.6038	$862.62	$862.65	$862.60