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	$33.57	12.172%	$37.6561	$37.66	$37.65	$37.70
Purchase #2	$40.61	10.606%	$44.9171	$44.92	$44.90	$44.90
Purchase #3	$117.65	11.102%	$130.7115	$130.71	$130.70	$130.70
Purchase #4	$45.39	11.510%	$50.6144	$50.61	$50.60	$50.60
Purchase #5	$164.61	12.344%	$184.9295	$184.93	$184.95	$184.90
Purchase #6	$152.53	12.113%	$171.006	$171.01	$171.00	$171.00
Purchase #7	$21.40	4.680%	$22.4015	$22.40	$22.40	$22.40
7 purchase totals =	$575.76		$642.2361	$642.24	$642.20	$642.20