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	$123.87	12.575%	$139.4467	$139.45	$139.45	$139.40
Purchase #2	$180.25	5.442%	$190.0592	$190.06	$190.05	$190.10
Purchase #3	$178.87	6.537%	$190.5627	$190.56	$190.55	$190.60
Purchase #4	$185.39	10.866%	$205.5345	$205.53	$205.55	$205.50
Purchase #5	$10.73	6.321%	$11.4082	$11.41	$11.40	$11.40
Purchase #6	$221.92	11.323%	$247.048	$247.05	$247.05	$247.00
Purchase #7	$39.52	13.507%	$44.858	$44.86	$44.85	$44.90
7 purchase totals =	$940.55		$1,028.9173	$1,028.92	$1,028.90	$1,028.90