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	$211.79	13.810%	$241.0382	$241.04	$241.05	$241.00
Purchase #2	$133.55	5.134%	$140.4065	$140.41	$140.40	$140.40
Purchase #3	$157.75	9.110%	$172.121	$172.12	$172.10	$172.10
Purchase #4	$146.51	13.282%	$165.9695	$165.97	$165.95	$166.00
Purchase #5	$187.72	9.650%	$205.835	$205.84	$205.85	$205.80
Purchase #6	$85.72	3.480%	$88.7031	$88.70	$88.70	$88.70
Purchase #7	$97.85	11.547%	$109.1487	$109.15	$109.15	$109.10
7 purchase totals =	$1,020.89		$1,123.2220	$1,123.23	$1,123.20	$1,123.10