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	$41.41	8.265%	$44.8325	$44.83	$44.85	$44.80
Purchase #2	$104.71	3.259%	$108.1225	$108.12	$108.10	$108.10
Purchase #3	$204.25	8.507%	$221.6255	$221.63	$221.65	$221.60
Purchase #4	$98.59	3.507%	$102.0476	$102.05	$102.05	$102.00
Purchase #5	$88.94	13.126%	$100.6143	$100.61	$100.60	$100.60
Purchase #6	$47.42	8.784%	$51.5854	$51.59	$51.60	$51.60
Purchase #7	$34.43	6.363%	$36.6208	$36.62	$36.60	$36.60
7 purchase totals =	$619.75		$665.4486	$665.45	$665.45	$665.30