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	$90.69	3.430%	$93.8007	$93.80	$93.80	$93.80
Purchase #2	$37.80	12.735%	$42.6138	$42.61	$42.60	$42.60
Purchase #3	$39.73	5.661%	$41.9791	$41.98	$42.00	$42.00
Purchase #4	$185.75	13.196%	$210.2616	$210.26	$210.25	$210.30
Purchase #5	$234.41	10.235%	$258.4019	$258.40	$258.40	$258.40
Purchase #6	$147.50	8.757%	$160.4166	$160.42	$160.40	$160.40
Purchase #7	$126.57	10.719%	$140.137	$140.14	$140.15	$140.10
7 purchase totals =	$862.45		$947.6107	$947.61	$947.60	$947.60