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	$41.78	8.498%	$45.3305	$45.33	$45.35	$45.30
Purchase #2	$35.96	4.354%	$37.5257	$37.53	$37.55	$37.50
Purchase #3	$172.64	9.603%	$189.2186	$189.22	$189.20	$189.20
Purchase #4	$223.80	5.343%	$235.7576	$235.76	$235.75	$235.80
Purchase #5	$123.47	13.103%	$139.6483	$139.65	$139.65	$139.60
Purchase #6	$37.91	11.520%	$42.2772	$42.28	$42.30	$42.30
Purchase #7	$60.98	3.576%	$63.1606	$63.16	$63.15	$63.20
7 purchase totals =	$696.54		$752.9185	$752.93	$752.95	$752.90