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	$89.78	11.605%	$100.199	$100.20	$100.20	$100.20
Purchase #2	$173.58	6.311%	$184.5346	$184.53	$184.55	$184.50
Purchase #3	$137.73	10.815%	$152.6255	$152.63	$152.65	$152.60
Purchase #4	$153.77	10.158%	$169.39	$169.39	$169.40	$169.40
Purchase #5	$138.34	9.304%	$151.2112	$151.21	$151.20	$151.20
Purchase #6	$23.59	12.789%	$26.6069	$26.61	$26.60	$26.60
Purchase #7	$46.84	6.528%	$49.8977	$49.90	$49.90	$49.90
7 purchase totals =	$763.63		$834.4649	$834.47	$834.50	$834.40