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	$40.75	6.401%	$43.3584	$43.36	$43.35	$43.40
Purchase #2	$111.76	9.637%	$122.5303	$122.53	$122.55	$122.50
Purchase #3	$148.81	7.438%	$159.8785	$159.88	$159.90	$159.90
Purchase #4	$34.36	8.180%	$37.1706	$37.17	$37.15	$37.20
Purchase #5	$29.67	13.398%	$33.6452	$33.65	$33.65	$33.60
Purchase #6	$147.50	4.576%	$154.2496	$154.25	$154.25	$154.20
Purchase #7	$53.32	12.137%	$59.7914	$59.79	$59.80	$59.80
7 purchase totals =	$566.17		$610.6240	$610.63	$610.65	$610.60