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	$170.89	7.854%	$184.3117	$184.31	$184.30	$184.30
Purchase #2	$16.94	7.635%	$18.2334	$18.23	$18.25	$18.20
Purchase #3	$42.72	9.386%	$46.7297	$46.73	$46.75	$46.70
Purchase #4	$140.63	13.863%	$160.1255	$160.13	$160.15	$160.10
Purchase #5	$139.52	5.333%	$146.9606	$146.96	$146.95	$147.00
Purchase #6	$121.56	13.140%	$137.533	$137.53	$137.55	$137.50
Purchase #7	$59.32	12.853%	$66.9444	$66.94	$66.95	$66.90
7 purchase totals =	$691.58		$760.8383	$760.83	$760.90	$760.70