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	$225.95	10.703%	$250.1334	$250.13	$250.15	$250.10
Purchase #2	$210.71	13.121%	$238.3573	$238.36	$238.35	$238.40
Purchase #3	$93.86	10.453%	$103.6712	$103.67	$103.65	$103.70
Purchase #4	$175.48	8.248%	$189.9536	$189.95	$189.95	$190.00
Purchase #5	$45.30	10.614%	$50.1081	$50.11	$50.10	$50.10
Purchase #6	$167.88	3.181%	$173.2203	$173.22	$173.20	$173.20
Purchase #7	$132.32	11.211%	$147.1544	$147.15	$147.15	$147.20
7 purchase totals =	$1,051.50		$1,152.5983	$1,152.59	$1,152.55	$1,152.70