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	$22.60	7.126%	$24.2105	$24.21	$24.20	$24.20
Purchase #2	$15.35	13.483%	$17.4196	$17.42	$17.40	$17.40
Purchase #3	$70.33	3.235%	$72.6052	$72.61	$72.60	$72.60
Purchase #4	$197.63	9.700%	$216.8001	$216.80	$216.80	$216.80
Purchase #5	$32.46	10.399%	$35.8355	$35.84	$35.85	$35.80
Purchase #6	$82.86	9.610%	$90.8228	$90.82	$90.80	$90.80
Purchase #7	$187.84	11.485%	$209.4134	$209.41	$209.40	$209.40
7 purchase totals =	$609.07		$667.1071	$667.11	$667.05	$667.00