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	$42.35	3.697%	$43.9157	$43.92	$43.90	$43.90
Purchase #2	$160.26	3.196%	$165.3819	$165.38	$165.40	$165.40
Purchase #3	$33.25	7.782%	$35.8375	$35.84	$35.85	$35.80
Purchase #4	$39.47	6.830%	$42.1658	$42.17	$42.15	$42.20
Purchase #5	$93.43	6.102%	$99.1311	$99.13	$99.15	$99.10
Purchase #6	$185.74	7.754%	$200.1423	$200.14	$200.15	$200.10
Purchase #7	$195.42	13.249%	$221.3112	$221.31	$221.30	$221.30
7 purchase totals =	$749.92		$807.8855	$807.89	$807.90	$807.80