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	$76.33	6.668%	$81.4197	$81.42	$81.40	$81.40
Purchase #2	$48.52	13.363%	$55.0037	$55.00	$55.00	$55.00
Purchase #3	$86.46	8.120%	$93.4806	$93.48	$93.50	$93.50
Purchase #4	$32.57	13.794%	$37.0627	$37.06	$37.05	$37.10
Purchase #5	$247.98	12.346%	$278.5956	$278.60	$278.60	$278.60
Purchase #6	$39.55	8.355%	$42.8544	$42.85	$42.85	$42.90
Purchase #7	$77.32	8.548%	$83.9293	$83.93	$83.95	$83.90
7 purchase totals =	$608.73		$672.3460	$672.34	$672.35	$672.40