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	$200.64	12.581%	$225.8825	$225.88	$225.90	$225.90
Purchase #2	$242.30	12.330%	$272.1756	$272.18	$272.20	$272.20
Purchase #3	$107.84	11.784%	$120.5479	$120.55	$120.55	$120.50
Purchase #4	$29.36	8.763%	$31.9328	$31.93	$31.95	$31.90
Purchase #5	$70.93	10.456%	$78.3464	$78.35	$78.35	$78.30
Purchase #6	$18.84	13.162%	$21.3197	$21.32	$21.30	$21.30
Purchase #7	$156.50	6.434%	$166.5692	$166.57	$166.55	$166.60
7 purchase totals =	$826.41		$916.7741	$916.78	$916.80	$916.70