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	$50.59	3.376%	$52.2979	$52.30	$52.30	$52.30
Purchase #2	$37.32	8.603%	$40.5306	$40.53	$40.55	$40.50
Purchase #3	$235.86	3.742%	$244.6859	$244.69	$244.70	$244.70
Purchase #4	$222.34	10.458%	$245.5923	$245.59	$245.60	$245.60
Purchase #5	$200.33	12.277%	$224.9245	$224.92	$224.90	$224.90
Purchase #6	$74.62	12.165%	$83.6975	$83.70	$83.70	$83.70
Purchase #7	$170.47	11.110%	$189.4092	$189.41	$189.40	$189.40
7 purchase totals =	$991.53		$1,081.1379	$1,081.14	$1,081.15	$1,081.10