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	$47.88	12.368%	$53.8018	$53.80	$53.80	$53.80
Purchase #2	$138.91	5.764%	$146.9168	$146.92	$146.90	$146.90
Purchase #3	$33.34	13.428%	$37.8169	$37.82	$37.80	$37.80
Purchase #4	$37.58	12.111%	$42.1313	$42.13	$42.15	$42.10
Purchase #5	$241.52	6.206%	$256.5087	$256.51	$256.50	$256.50
Purchase #6	$75.49	10.581%	$83.4776	$83.48	$83.50	$83.50
Purchase #7	$150.95	12.528%	$169.861	$169.86	$169.85	$169.90
7 purchase totals =	$725.67		$790.5141	$790.52	$790.50	$790.50