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	$15.74	13.419%	$17.8522	$17.85	$17.85	$17.90
Purchase #2	$144.43	9.409%	$158.0194	$158.02	$158.00	$158.00
Purchase #3	$240.32	6.778%	$256.6089	$256.61	$256.60	$256.60
Purchase #4	$44.51	3.126%	$45.9014	$45.90	$45.90	$45.90
Purchase #5	$36.85	11.568%	$41.1128	$41.11	$41.10	$41.10
Purchase #6	$90.94	7.863%	$98.0906	$98.09	$98.10	$98.10
Purchase #7	$240.73	9.503%	$263.6066	$263.61	$263.60	$263.60
7 purchase totals =	$813.52		$881.1919	$881.19	$881.15	$881.20