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	$17.81	4.301%	$18.576	$18.58	$18.60	$18.60
Purchase #2	$36.68	3.208%	$37.8567	$37.86	$37.85	$37.90
Purchase #3	$237.81	5.616%	$251.1654	$251.17	$251.15	$251.20
Purchase #4	$42.80	11.630%	$47.7776	$47.78	$47.80	$47.80
Purchase #5	$89.47	3.468%	$92.5728	$92.57	$92.55	$92.60
Purchase #6	$142.45	7.529%	$153.1751	$153.18	$153.20	$153.20
Purchase #7	$10.31	11.483%	$11.4939	$11.49	$11.50	$11.50
7 purchase totals =	$577.33		$612.6175	$612.63	$612.65	$612.80