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	$238.88	13.238%	$270.5029	$270.50	$270.50	$270.50
Purchase #2	$11.57	10.189%	$12.7489	$12.75	$12.75	$12.70
Purchase #3	$63.32	11.282%	$70.4638	$70.46	$70.45	$70.50
Purchase #4	$141.49	8.352%	$153.3072	$153.31	$153.30	$153.30
Purchase #5	$37.50	8.853%	$40.8199	$40.82	$40.80	$40.80
Purchase #6	$199.60	11.288%	$222.1308	$222.13	$222.15	$222.10
Purchase #7	$161.33	4.451%	$168.5108	$168.51	$168.50	$168.50
7 purchase totals =	$853.69		$938.4843	$938.48	$938.45	$938.40