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	$103.39	12.524%	$116.3386	$116.34	$116.35	$116.30
Purchase #2	$234.89	9.232%	$256.575	$256.58	$256.60	$256.60
Purchase #3	$137.71	12.869%	$155.4319	$155.43	$155.45	$155.40
Purchase #4	$88.25	11.554%	$98.4464	$98.45	$98.45	$98.40
Purchase #5	$39.33	3.412%	$40.6719	$40.67	$40.65	$40.70
Purchase #6	$174.69	10.351%	$192.7722	$192.77	$192.75	$192.80
Purchase #7	$145.68	13.489%	$165.3308	$165.33	$165.35	$165.30
7 purchase totals =	$923.94		$1,025.5668	$1,025.57	$1,025.60	$1,025.50