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	$91.68	7.312%	$98.3836	$98.38	$98.40	$98.40
Purchase #2	$45.73	9.819%	$50.2202	$50.22	$50.20	$50.20
Purchase #3	$32.71	11.429%	$36.4484	$36.45	$36.45	$36.40
Purchase #4	$55.47	13.404%	$62.9052	$62.91	$62.90	$62.90
Purchase #5	$140.33	11.248%	$156.1143	$156.11	$156.10	$156.10
Purchase #6	$56.33	3.224%	$58.1461	$58.15	$58.15	$58.10
Purchase #7	$33.53	13.492%	$38.0539	$38.05	$38.05	$38.10
7 purchase totals =	$455.78		$500.2717	$500.27	$500.25	$500.20