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	$46.95	6.501%	$50.0022	$50.00	$50.00	$50.00
Purchase #2	$199.40	8.475%	$216.2992	$216.30	$216.30	$216.30
Purchase #3	$139.46	8.153%	$150.8302	$150.83	$150.85	$150.80
Purchase #4	$198.92	4.692%	$208.2533	$208.25	$208.25	$208.30
Purchase #5	$68.53	13.619%	$77.8631	$77.86	$77.85	$77.90
Purchase #6	$56.63	4.277%	$59.0521	$59.05	$59.05	$59.10
Purchase #7	$72.98	5.398%	$76.9195	$76.92	$76.90	$76.90
7 purchase totals =	$782.87		$839.2196	$839.21	$839.20	$839.30