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	$243.51	13.243%	$275.758	$275.76	$275.75	$275.80
Purchase #2	$204.82	4.604%	$214.2499	$214.25	$214.25	$214.20
Purchase #3	$87.44	3.687%	$90.6639	$90.66	$90.65	$90.70
Purchase #4	$56.37	13.347%	$63.8937	$63.89	$63.90	$63.90
Purchase #5	$69.82	9.362%	$76.3565	$76.36	$76.35	$76.40
Purchase #6	$28.86	11.446%	$32.1633	$32.16	$32.15	$32.20
Purchase #7	$119.58	5.624%	$126.3052	$126.31	$126.30	$126.30
7 purchase totals =	$810.40		$879.3905	$879.39	$879.35	$879.50