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	$62.39	7.438%	$67.0306	$67.03	$67.05	$67.00
Purchase #2	$86.29	9.702%	$94.6619	$94.66	$94.65	$94.70
Purchase #3	$47.89	10.419%	$52.8797	$52.88	$52.90	$52.90
Purchase #4	$66.36	12.810%	$74.8607	$74.86	$74.85	$74.90
Purchase #5	$204.71	13.284%	$231.9037	$231.90	$231.90	$231.90
Purchase #6	$75.35	9.412%	$82.4419	$82.44	$82.45	$82.40
Purchase #7	$63.79	12.364%	$71.677	$71.68	$71.70	$71.70
7 purchase totals =	$606.78		$675.4555	$675.45	$675.50	$675.50