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	$246.50	11.276%	$274.2953	$274.30	$274.30	$274.30
Purchase #2	$215.48	10.872%	$238.907	$238.91	$238.90	$238.90
Purchase #3	$15.86	4.698%	$16.6051	$16.61	$16.60	$16.60
Purchase #4	$34.80	10.114%	$38.3197	$38.32	$38.30	$38.30
Purchase #5	$41.54	9.549%	$45.5067	$45.51	$45.50	$45.50
Purchase #6	$6.98	8.580%	$7.5789	$7.58	$7.60	$7.60
Purchase #7	$20.70	10.598%	$22.8938	$22.89	$22.90	$22.90
7 purchase totals =	$581.86		$644.1065	$644.12	$644.10	$644.10