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	$53.41	9.188%	$58.3173	$58.32	$58.30	$58.30
Purchase #2	$62.49	6.164%	$66.3419	$66.34	$66.35	$66.30
Purchase #3	$135.61	8.156%	$146.6704	$146.67	$146.65	$146.70
Purchase #4	$246.54	11.521%	$274.9439	$274.94	$274.95	$274.90
Purchase #5	$69.83	11.632%	$77.9526	$77.95	$77.95	$78.00
Purchase #6	$77.27	7.831%	$83.321	$83.32	$83.30	$83.30
Purchase #7	$56.75	4.860%	$59.5081	$59.51	$59.50	$59.50
7 purchase totals =	$701.90		$767.0552	$767.05	$767.00	$767.00