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	$46.56	8.683%	$50.6028	$50.60	$50.60	$50.60
Purchase #2	$92.53	13.333%	$104.867	$104.87	$104.85	$104.90
Purchase #3	$148.29	6.102%	$157.3387	$157.34	$157.35	$157.30
Purchase #4	$171.87	8.191%	$185.9479	$185.95	$185.95	$185.90
Purchase #5	$171.43	9.287%	$187.3507	$187.35	$187.35	$187.40
Purchase #6	$126.82	11.460%	$141.3536	$141.35	$141.35	$141.40
Purchase #7	$76.62	11.290%	$85.2704	$85.27	$85.25	$85.30
7 purchase totals =	$834.12		$912.7311	$912.73	$912.70	$912.80