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	$237.74	7.388%	$255.3042	$255.30	$255.30	$255.30
Purchase #2	$11.37	6.504%	$12.1095	$12.11	$12.10	$12.10
Purchase #3	$116.51	4.368%	$121.5992	$121.60	$121.60	$121.60
Purchase #4	$110.30	11.535%	$123.0231	$123.02	$123.00	$123.00
Purchase #5	$154.90	8.143%	$167.5135	$167.51	$167.50	$167.50
Purchase #6	$116.83	11.387%	$130.1334	$130.13	$130.15	$130.10
Purchase #7	$136.92	3.832%	$142.1668	$142.17	$142.15	$142.20
7 purchase totals =	$884.57		$951.8497	$951.84	$951.80	$951.80