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	$113.83	5.869%	$120.5107	$120.51	$120.50	$120.50
Purchase #2	$6.83	10.111%	$7.5206	$7.52	$7.50	$7.50
Purchase #3	$87.77	10.613%	$97.085	$97.09	$97.10	$97.10
Purchase #4	$12.71	3.540%	$13.1599	$13.16	$13.15	$13.20
Purchase #5	$52.57	4.698%	$55.0397	$55.04	$55.05	$55.00
Purchase #6	$124.51	7.806%	$134.2293	$134.23	$134.25	$134.20
Purchase #7	$75.37	13.810%	$85.7786	$85.78	$85.80	$85.80
7 purchase totals =	$473.59		$513.3238	$513.33	$513.35	$513.30