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	$220.75	12.530%	$248.41	$248.41	$248.40	$248.40
Purchase #2	$75.84	12.222%	$85.1092	$85.11	$85.10	$85.10
Purchase #3	$69.89	3.733%	$72.499	$72.50	$72.50	$72.50
Purchase #4	$176.35	9.700%	$193.456	$193.46	$193.45	$193.50
Purchase #5	$190.43	9.347%	$208.2295	$208.23	$208.25	$208.20
Purchase #6	$61.59	3.760%	$63.9058	$63.91	$63.90	$63.90
Purchase #7	$24.40	12.502%	$27.4505	$27.45	$27.45	$27.50
7 purchase totals =	$819.25		$899.0600	$899.07	$899.05	$899.10