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	$155.54	11.569%	$173.5344	$173.53	$173.55	$173.50
Purchase #2	$34.72	9.594%	$38.051	$38.05	$38.05	$38.10
Purchase #3	$59.95	8.247%	$64.8941	$64.89	$64.90	$64.90
Purchase #4	$57.79	6.467%	$61.5273	$61.53	$61.55	$61.50
Purchase #5	$156.80	4.730%	$164.2166	$164.22	$164.20	$164.20
Purchase #6	$126.41	3.466%	$130.7914	$130.79	$130.80	$130.80
Purchase #7	$25.69	11.740%	$28.706	$28.71	$28.70	$28.70
7 purchase totals =	$616.90		$661.7208	$661.72	$661.75	$661.70