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	$130.61	12.146%	$146.4739	$146.47	$146.45	$146.50
Purchase #2	$110.72	11.680%	$123.6521	$123.65	$123.65	$123.70
Purchase #3	$30.60	9.420%	$33.4825	$33.48	$33.50	$33.50
Purchase #4	$205.33	8.626%	$223.0418	$223.04	$223.05	$223.00
Purchase #5	$92.49	12.771%	$104.3019	$104.30	$104.30	$104.30
Purchase #6	$142.99	7.473%	$153.6756	$153.68	$153.70	$153.70
Purchase #7	$169.85	12.651%	$191.3377	$191.34	$191.35	$191.30
7 purchase totals =	$882.59		$975.9655	$975.96	$976.00	$976.00