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	$11.78	10.528%	$13.0202	$13.02	$13.00	$13.00
Purchase #2	$37.37	13.583%	$42.446	$42.45	$42.45	$42.40
Purchase #3	$213.26	7.139%	$228.4846	$228.48	$228.50	$228.50
Purchase #4	$107.78	11.323%	$119.9839	$119.98	$120.00	$120.00
Purchase #5	$201.58	10.198%	$222.1371	$222.14	$222.15	$222.10
Purchase #6	$243.27	8.323%	$263.5174	$263.52	$263.50	$263.50
Purchase #7	$125.46	4.593%	$131.2224	$131.22	$131.20	$131.20
7 purchase totals =	$940.50		$1,020.8116	$1,020.81	$1,020.80	$1,020.70