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	$63.63	5.501%	$67.1303	$67.13	$67.15	$67.10
Purchase #2	$52.38	13.544%	$59.4743	$59.47	$59.45	$59.50
Purchase #3	$95.89	4.741%	$100.4361	$100.44	$100.45	$100.40
Purchase #4	$91.57	5.473%	$96.5816	$96.58	$96.60	$96.60
Purchase #5	$26.68	6.642%	$28.4521	$28.45	$28.45	$28.50
Purchase #6	$21.37	3.243%	$22.063	$22.06	$22.05	$22.10
Purchase #7	$209.77	13.633%	$238.3679	$238.37	$238.35	$238.40
7 purchase totals =	$561.29		$612.5053	$612.50	$612.50	$612.60