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	$81.69	12.548%	$91.9405	$91.94	$91.95	$91.90
Purchase #2	$73.63	13.620%	$83.6584	$83.66	$83.65	$83.70
Purchase #3	$238.59	5.634%	$252.0322	$252.03	$252.05	$252.00
Purchase #4	$37.46	7.143%	$40.1358	$40.14	$40.15	$40.10
Purchase #5	$103.89	7.431%	$111.6101	$111.61	$111.60	$111.60
Purchase #6	$123.98	7.133%	$132.8235	$132.82	$132.80	$132.80
Purchase #7	$244.83	10.154%	$269.69	$269.69	$269.70	$269.70
7 purchase totals =	$904.07		$981.8905	$981.89	$981.90	$981.80