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	$74.74	7.340%	$80.2259	$80.23	$80.25	$80.20
Purchase #2	$38.29	6.761%	$40.8788	$40.88	$40.90	$40.90
Purchase #3	$15.89	3.837%	$16.4997	$16.50	$16.50	$16.50
Purchase #4	$40.69	11.756%	$45.4735	$45.47	$45.45	$45.50
Purchase #5	$168.73	13.409%	$191.355	$191.36	$191.35	$191.40
Purchase #6	$196.55	4.755%	$205.896	$205.90	$205.90	$205.90
Purchase #7	$235.85	8.191%	$255.1685	$255.17	$255.15	$255.20
7 purchase totals =	$770.74		$835.4974	$835.51	$835.50	$835.60