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	$170.56	12.646%	$192.129	$192.13	$192.15	$192.10
Purchase #2	$86.30	4.210%	$89.9332	$89.93	$89.95	$89.90
Purchase #3	$189.96	9.733%	$208.4488	$208.45	$208.45	$208.40
Purchase #4	$33.63	3.669%	$34.8639	$34.86	$34.85	$34.90
Purchase #5	$211.81	4.753%	$221.8773	$221.88	$221.90	$221.90
Purchase #6	$192.46	7.193%	$206.3036	$206.30	$206.30	$206.30
Purchase #7	$127.44	13.174%	$144.2289	$144.23	$144.25	$144.20
7 purchase totals =	$1,012.16		$1,097.7847	$1,097.78	$1,097.85	$1,097.70