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	$46.42	9.185%	$50.6837	$50.68	$50.70	$50.70
Purchase #2	$34.99	7.234%	$37.5212	$37.52	$37.50	$37.50
Purchase #3	$46.83	9.693%	$51.3692	$51.37	$51.35	$51.40
Purchase #4	$206.97	11.672%	$231.1275	$231.13	$231.15	$231.10
Purchase #5	$26.38	8.279%	$28.564	$28.56	$28.55	$28.60
Purchase #6	$65.35	11.449%	$72.8319	$72.83	$72.85	$72.80
Purchase #7	$28.75	10.350%	$31.7256	$31.73	$31.75	$31.70
7 purchase totals =	$455.69		$503.8231	$503.82	$503.85	$503.80