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	$30.60	5.329%	$32.2307	$32.23	$32.25	$32.20
Purchase #2	$144.63	9.181%	$157.9085	$157.91	$157.90	$157.90
Purchase #3	$200.80	12.296%	$225.4904	$225.49	$225.50	$225.50
Purchase #4	$237.73	4.261%	$247.8597	$247.86	$247.85	$247.90
Purchase #5	$125.35	13.581%	$142.3738	$142.37	$142.35	$142.40
Purchase #6	$78.56	6.754%	$83.8659	$83.87	$83.85	$83.90
Purchase #7	$49.40	10.851%	$54.7604	$54.76	$54.75	$54.80
7 purchase totals =	$867.07		$944.4894	$944.49	$944.45	$944.60