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	$242.50	12.402%	$272.5749	$272.57	$272.55	$272.60
Purchase #2	$231.36	13.431%	$262.434	$262.43	$262.45	$262.40
Purchase #3	$100.57	3.839%	$104.4309	$104.43	$104.45	$104.40
Purchase #4	$108.78	9.319%	$118.9172	$118.92	$118.90	$118.90
Purchase #5	$59.83	11.640%	$66.7942	$66.79	$66.80	$66.80
Purchase #6	$110.95	8.851%	$120.7702	$120.77	$120.75	$120.80
Purchase #7	$208.57	7.371%	$223.9437	$223.94	$223.95	$223.90
7 purchase totals =	$1,062.56		$1,169.8651	$1,169.85	$1,169.85	$1,169.80