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	$138.79	5.779%	$146.8107	$146.81	$146.80	$146.80
Purchase #2	$82.84	9.169%	$90.4356	$90.44	$90.45	$90.40
Purchase #3	$28.57	13.700%	$32.4841	$32.48	$32.50	$32.50
Purchase #4	$160.84	6.548%	$171.3718	$171.37	$171.35	$171.40
Purchase #5	$146.85	9.429%	$160.6965	$160.70	$160.70	$160.70
Purchase #6	$53.95	6.188%	$57.2884	$57.29	$57.30	$57.30
Purchase #7	$95.60	5.141%	$100.5148	$100.51	$100.50	$100.50
7 purchase totals =	$707.44		$759.6019	$759.60	$759.60	$759.60