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	$83.28	7.442%	$89.4777	$89.48	$89.50	$89.50
Purchase #2	$188.82	4.227%	$196.8014	$196.80	$196.80	$196.80
Purchase #3	$196.84	8.621%	$213.8096	$213.81	$213.80	$213.80
Purchase #4	$157.30	11.657%	$175.6365	$175.64	$175.65	$175.60
Purchase #5	$78.88	8.363%	$85.4767	$85.48	$85.50	$85.50
Purchase #6	$59.53	5.667%	$62.9036	$62.90	$62.90	$62.90
Purchase #7	$121.77	9.602%	$133.4624	$133.46	$133.45	$133.50
7 purchase totals =	$886.42		$957.5679	$957.57	$957.60	$957.60