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	$97.66	3.785%	$101.3564	$101.36	$101.35	$101.40
Purchase #2	$132.72	9.197%	$144.9263	$144.93	$144.95	$144.90
Purchase #3	$153.27	10.816%	$169.8477	$169.85	$169.85	$169.80
Purchase #4	$155.25	6.256%	$164.9624	$164.96	$164.95	$165.00
Purchase #5	$100.92	10.678%	$111.6962	$111.70	$111.70	$111.70
Purchase #6	$234.47	6.856%	$250.5453	$250.55	$250.55	$250.50
Purchase #7	$13.31	5.502%	$14.0423	$14.04	$14.05	$14.00
7 purchase totals =	$887.60		$957.3766	$957.39	$957.40	$957.30