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	$203.72	13.346%	$230.9085	$230.91	$230.90	$230.90
Purchase #2	$195.58	13.756%	$222.484	$222.48	$222.50	$222.50
Purchase #3	$28.46	13.144%	$32.2008	$32.20	$32.20	$32.20
Purchase #4	$34.96	10.610%	$38.6693	$38.67	$38.65	$38.70
Purchase #5	$114.48	3.405%	$118.378	$118.38	$118.40	$118.40
Purchase #6	$35.94	5.118%	$37.7794	$37.78	$37.80	$37.80
Purchase #7	$152.97	12.176%	$171.5956	$171.60	$171.60	$171.60
7 purchase totals =	$766.11		$852.0156	$852.02	$852.05	$852.10