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	$62.88	11.653%	$70.2074	$70.21	$70.20	$70.20
Purchase #2	$154.49	11.243%	$171.8593	$171.86	$171.85	$171.90
Purchase #3	$239.77	8.582%	$260.3471	$260.35	$260.35	$260.30
Purchase #4	$132.55	7.590%	$142.6105	$142.61	$142.60	$142.60
Purchase #5	$179.25	6.570%	$191.0267	$191.03	$191.05	$191.00
Purchase #6	$9.49	7.787%	$10.229	$10.23	$10.25	$10.20
Purchase #7	$44.38	3.266%	$45.8295	$45.83	$45.85	$45.80
7 purchase totals =	$822.81		$892.1095	$892.12	$892.15	$892.00