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	$29.35	11.470%	$32.7164	$32.72	$32.70	$32.70
Purchase #2	$58.86	12.172%	$66.0244	$66.02	$66.00	$66.00
Purchase #3	$184.73	12.662%	$208.1205	$208.12	$208.10	$208.10
Purchase #4	$54.68	8.726%	$59.4514	$59.45	$59.45	$59.50
Purchase #5	$100.34	9.486%	$109.8583	$109.86	$109.85	$109.90
Purchase #6	$232.73	12.847%	$262.6288	$262.63	$262.65	$262.60
Purchase #7	$69.91	9.530%	$76.5724	$76.57	$76.55	$76.60
7 purchase totals =	$730.60		$815.3722	$815.37	$815.30	$815.40