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	$228.85	12.239%	$256.859	$256.86	$256.85	$256.90
Purchase #2	$47.91	5.420%	$50.5067	$50.51	$50.50	$50.50
Purchase #3	$90.54	9.750%	$99.3677	$99.37	$99.35	$99.40
Purchase #4	$62.34	8.352%	$67.5466	$67.55	$67.55	$67.50
Purchase #5	$149.56	10.299%	$164.9632	$164.96	$164.95	$165.00
Purchase #6	$126.54	4.742%	$132.5405	$132.54	$132.55	$132.50
Purchase #7	$26.28	8.151%	$28.4221	$28.42	$28.40	$28.40
7 purchase totals =	$732.02		$800.2058	$800.21	$800.15	$800.20