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	$216.91	13.603%	$246.4163	$246.42	$246.40	$246.40
Purchase #2	$83.48	12.477%	$93.8958	$93.90	$93.90	$93.90
Purchase #3	$140.45	11.300%	$156.3209	$156.32	$156.30	$156.30
Purchase #4	$32.34	6.595%	$34.4728	$34.47	$34.45	$34.50
Purchase #5	$97.55	12.418%	$109.6638	$109.66	$109.65	$109.70
Purchase #6	$78.53	8.712%	$85.3715	$85.37	$85.35	$85.40
Purchase #7	$32.60	3.753%	$33.8235	$33.82	$33.80	$33.80
7 purchase totals =	$681.86		$759.9646	$759.96	$759.85	$760.00