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	$85.73	4.537%	$89.6196	$89.62	$89.60	$89.60
Purchase #2	$237.89	11.227%	$264.5979	$264.60	$264.60	$264.60
Purchase #3	$11.77	11.363%	$13.1074	$13.11	$13.10	$13.10
Purchase #4	$35.34	6.355%	$37.5859	$37.59	$37.60	$37.60
Purchase #5	$194.81	8.453%	$211.2773	$211.28	$211.30	$211.30
Purchase #6	$179.57	5.655%	$189.7247	$189.72	$189.70	$189.70
Purchase #7	$242.59	13.148%	$274.4857	$274.49	$274.50	$274.50
7 purchase totals =	$987.70		$1,080.3985	$1,080.41	$1,080.40	$1,080.40