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	$78.82	3.417%	$81.5133	$81.51	$81.50	$81.50
Purchase #2	$208.25	7.842%	$224.581	$224.58	$224.60	$224.60
Purchase #3	$236.98	4.563%	$247.7934	$247.79	$247.80	$247.80
Purchase #4	$69.38	7.517%	$74.5953	$74.60	$74.60	$74.60
Purchase #5	$30.74	4.548%	$32.1381	$32.14	$32.15	$32.10
Purchase #6	$81.55	10.228%	$89.8909	$89.89	$89.90	$89.90
Purchase #7	$231.86	9.450%	$253.7708	$253.77	$253.75	$253.80
7 purchase totals =	$937.58		$1,004.2828	$1,004.28	$1,004.30	$1,004.30