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	$59.94	11.614%	$66.9014	$66.90	$66.90	$66.90
Purchase #2	$90.35	12.835%	$101.9464	$101.95	$101.95	$101.90
Purchase #3	$138.41	8.438%	$150.089	$150.09	$150.10	$150.10
Purchase #4	$117.51	12.130%	$131.764	$131.76	$131.75	$131.80
Purchase #5	$204.35	6.435%	$217.4999	$217.50	$217.50	$217.50
Purchase #6	$87.53	9.591%	$95.925	$95.93	$95.95	$95.90
Purchase #7	$84.39	7.723%	$90.9074	$90.91	$90.90	$90.90
7 purchase totals =	$782.48		$855.0331	$855.04	$855.05	$855.00