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	$39.98	5.622%	$42.2277	$42.23	$42.25	$42.20
Purchase #2	$78.62	9.205%	$85.857	$85.86	$85.85	$85.90
Purchase #3	$86.81	10.254%	$95.7115	$95.71	$95.70	$95.70
Purchase #4	$234.59	8.147%	$253.702	$253.70	$253.70	$253.70
Purchase #5	$62.69	12.261%	$70.3764	$70.38	$70.40	$70.40
Purchase #6	$98.54	13.129%	$111.4773	$111.48	$111.50	$111.50
Purchase #7	$9.57	13.358%	$10.8484	$10.85	$10.85	$10.80
7 purchase totals =	$610.80		$670.2003	$670.21	$670.25	$670.20