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	$136.88	6.536%	$145.8265	$145.83	$145.85	$145.80
Purchase #2	$91.32	4.484%	$95.4148	$95.41	$95.40	$95.40
Purchase #3	$88.65	13.847%	$100.9254	$100.93	$100.95	$100.90
Purchase #4	$38.48	10.597%	$42.5577	$42.56	$42.55	$42.60
Purchase #5	$213.40	7.146%	$228.6496	$228.65	$228.65	$228.60
Purchase #6	$21.65	12.419%	$24.3387	$24.34	$24.35	$24.30
Purchase #7	$35.62	13.325%	$40.3664	$40.37	$40.35	$40.40
7 purchase totals =	$626.00		$678.0791	$678.09	$678.10	$678.00