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	$95.71	4.565%	$100.0792	$100.08	$100.10	$100.10
Purchase #2	$198.87	8.817%	$216.4044	$216.40	$216.40	$216.40
Purchase #3	$102.49	13.645%	$116.4748	$116.47	$116.45	$116.50
Purchase #4	$20.68	9.659%	$22.6775	$22.68	$22.70	$22.70
Purchase #5	$54.73	8.754%	$59.5211	$59.52	$59.50	$59.50
Purchase #6	$47.66	7.185%	$51.0844	$51.08	$51.10	$51.10
Purchase #7	$88.67	6.140%	$94.1143	$94.11	$94.10	$94.10
7 purchase totals =	$608.81		$660.3557	$660.34	$660.35	$660.40