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	$7.51	3.168%	$7.7479	$7.75	$7.75	$7.70
Purchase #2	$227.32	8.787%	$247.2946	$247.29	$247.30	$247.30
Purchase #3	$100.88	10.382%	$111.3534	$111.35	$111.35	$111.40
Purchase #4	$137.52	12.840%	$155.1776	$155.18	$155.20	$155.20
Purchase #5	$91.33	12.821%	$103.0394	$103.04	$103.05	$103.00
Purchase #6	$104.57	11.622%	$116.7231	$116.72	$116.70	$116.70
Purchase #7	$223.83	8.462%	$242.7705	$242.77	$242.75	$242.80
7 purchase totals =	$892.96		$984.1065	$984.10	$984.10	$984.10