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	$101.66	6.684%	$108.455	$108.46	$108.45	$108.50
Purchase #2	$186.35	4.405%	$194.5587	$194.56	$194.55	$194.60
Purchase #3	$198.82	3.722%	$206.2201	$206.22	$206.20	$206.20
Purchase #4	$59.48	9.121%	$64.9052	$64.91	$64.90	$64.90
Purchase #5	$11.76	12.765%	$13.2612	$13.26	$13.25	$13.30
Purchase #6	$56.66	8.480%	$61.4648	$61.46	$61.45	$61.50
Purchase #7	$165.40	12.105%	$185.4217	$185.42	$185.40	$185.40
7 purchase totals =	$780.13		$834.2867	$834.29	$834.20	$834.40