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	$45.67	6.444%	$48.613	$48.61	$48.60	$48.60
Purchase #2	$87.29	3.774%	$90.5843	$90.58	$90.60	$90.60
Purchase #3	$121.89	13.846%	$138.7669	$138.77	$138.75	$138.80
Purchase #4	$203.67	13.528%	$231.2225	$231.22	$231.20	$231.20
Purchase #5	$35.54	6.746%	$37.9375	$37.94	$37.95	$37.90
Purchase #6	$135.77	9.820%	$149.1026	$149.10	$149.10	$149.10
Purchase #7	$66.75	8.206%	$72.2275	$72.23	$72.25	$72.20
7 purchase totals =	$696.58		$768.4543	$768.45	$768.45	$768.40