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	$190.47	4.586%	$199.205	$199.21	$199.20	$199.20
Purchase #2	$135.47	7.128%	$145.1263	$145.13	$145.15	$145.10
Purchase #3	$130.31	9.765%	$143.0348	$143.03	$143.05	$143.00
Purchase #4	$41.51	8.496%	$45.0367	$45.04	$45.05	$45.00
Purchase #5	$156.51	12.283%	$175.7341	$175.73	$175.75	$175.70
Purchase #6	$85.81	10.505%	$94.8243	$94.82	$94.80	$94.80
Purchase #7	$61.59	6.412%	$65.5392	$65.54	$65.55	$65.50
7 purchase totals =	$801.67		$868.5004	$868.50	$868.55	$868.30