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	$119.80	6.520%	$127.611	$127.61	$127.60	$127.60
Purchase #2	$206.99	13.694%	$235.3352	$235.34	$235.35	$235.30
Purchase #3	$55.66	6.367%	$59.2039	$59.20	$59.20	$59.20
Purchase #4	$54.76	10.533%	$60.5279	$60.53	$60.55	$60.50
Purchase #5	$137.77	8.502%	$149.4832	$149.48	$149.50	$149.50
Purchase #6	$200.59	6.109%	$212.844	$212.84	$212.85	$212.80
Purchase #7	$40.97	3.775%	$42.5166	$42.52	$42.50	$42.50
7 purchase totals =	$816.54		$887.5218	$887.52	$887.55	$887.40