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	$53.39	5.714%	$56.4407	$56.44	$56.45	$56.40
Purchase #2	$163.25	10.401%	$180.2296	$180.23	$180.25	$180.20
Purchase #3	$177.83	12.874%	$200.7238	$200.72	$200.70	$200.70
Purchase #4	$45.86	10.172%	$50.5249	$50.52	$50.50	$50.50
Purchase #5	$168.34	13.137%	$190.4548	$190.45	$190.45	$190.50
Purchase #6	$13.46	12.379%	$15.1262	$15.13	$15.15	$15.10
Purchase #7	$88.94	12.332%	$99.9081	$99.91	$99.90	$99.90
7 purchase totals =	$711.07		$793.4081	$793.40	$793.40	$793.30