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	$99.58	12.439%	$111.9668	$111.97	$111.95	$112.00
Purchase #2	$71.71	6.310%	$76.2349	$76.23	$76.25	$76.20
Purchase #3	$129.28	7.655%	$139.1764	$139.18	$139.20	$139.20
Purchase #4	$13.53	8.761%	$14.7154	$14.72	$14.70	$14.70
Purchase #5	$50.25	3.255%	$51.8856	$51.89	$51.90	$51.90
Purchase #6	$123.31	11.159%	$137.0702	$137.07	$137.05	$137.10
Purchase #7	$69.96	12.729%	$78.8652	$78.87	$78.85	$78.90
7 purchase totals =	$557.62		$609.9145	$609.93	$609.90	$610.00