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	$57.90	13.136%	$65.5057	$65.51	$65.50	$65.50
Purchase #2	$94.46	5.452%	$99.61	$99.61	$99.60	$99.60
Purchase #3	$192.64	3.318%	$199.0318	$199.03	$199.05	$199.00
Purchase #4	$44.41	7.803%	$47.8753	$47.88	$47.90	$47.90
Purchase #5	$55.89	8.540%	$60.663	$60.66	$60.65	$60.70
Purchase #6	$32.55	12.485%	$36.6139	$36.61	$36.60	$36.60
Purchase #7	$130.30	12.108%	$146.0767	$146.08	$146.10	$146.10
7 purchase totals =	$608.15		$655.3764	$655.38	$655.40	$655.40