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	$128.53	8.498%	$139.4525	$139.45	$139.45	$139.50
Purchase #2	$166.37	11.401%	$185.3378	$185.34	$185.35	$185.30
Purchase #3	$192.90	9.164%	$210.5774	$210.58	$210.60	$210.60
Purchase #4	$219.29	4.790%	$229.794	$229.79	$229.80	$229.80
Purchase #5	$104.46	6.519%	$111.2697	$111.27	$111.25	$111.30
Purchase #6	$209.26	3.315%	$216.197	$216.20	$216.20	$216.20
Purchase #7	$220.85	9.625%	$242.1068	$242.11	$242.10	$242.10
7 purchase totals =	$1,241.66		$1,334.7352	$1,334.74	$1,334.75	$1,334.80