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	$39.33	5.702%	$41.5726	$41.57	$41.55	$41.60
Purchase #2	$145.76	12.766%	$164.3677	$164.37	$164.35	$164.40
Purchase #3	$126.50	4.646%	$132.3772	$132.38	$132.40	$132.40
Purchase #4	$18.50	10.428%	$20.4292	$20.43	$20.45	$20.40
Purchase #5	$50.51	8.595%	$54.8513	$54.85	$54.85	$54.90
Purchase #6	$71.46	9.857%	$78.5038	$78.50	$78.50	$78.50
Purchase #7	$24.77	13.490%	$28.1115	$28.11	$28.10	$28.10
7 purchase totals =	$476.83		$520.2133	$520.21	$520.20	$520.30