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	$37.83	12.198%	$42.4445	$42.44	$42.45	$42.40
Purchase #2	$201.36	5.679%	$212.7952	$212.80	$212.80	$212.80
Purchase #3	$39.59	6.683%	$42.2358	$42.24	$42.25	$42.20
Purchase #4	$221.63	5.853%	$234.602	$234.60	$234.60	$234.60
Purchase #5	$18.25	11.430%	$20.336	$20.34	$20.35	$20.30
Purchase #6	$138.34	8.851%	$150.5845	$150.58	$150.60	$150.60
Purchase #7	$184.35	3.513%	$190.8262	$190.83	$190.85	$190.80
7 purchase totals =	$841.35		$893.8242	$893.83	$893.90	$893.70