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	$224.58	6.373%	$238.8925	$238.89	$238.90	$238.90
Purchase #2	$83.68	9.598%	$91.7116	$91.71	$91.70	$91.70
Purchase #3	$244.76	12.376%	$275.0515	$275.05	$275.05	$275.10
Purchase #4	$61.58	6.853%	$65.8001	$65.80	$65.80	$65.80
Purchase #5	$47.87	6.181%	$50.8288	$50.83	$50.85	$50.80
Purchase #6	$250.51	12.499%	$281.8212	$281.82	$281.80	$281.80
Purchase #7	$28.38	13.340%	$32.1659	$32.17	$32.15	$32.20
7 purchase totals =	$941.36		$1,036.2716	$1,036.27	$1,036.25	$1,036.30