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	$140.85	7.106%	$150.8588	$150.86	$150.85	$150.90
Purchase #2	$81.60	9.178%	$89.0892	$89.09	$89.10	$89.10
Purchase #3	$66.32	7.738%	$71.4518	$71.45	$71.45	$71.50
Purchase #4	$83.57	10.654%	$92.4735	$92.47	$92.45	$92.50
Purchase #5	$210.67	10.222%	$232.2047	$232.20	$232.20	$232.20
Purchase #6	$180.50	10.338%	$199.1601	$199.16	$199.15	$199.20
Purchase #7	$9.84	9.578%	$10.7825	$10.78	$10.80	$10.80
7 purchase totals =	$773.35		$846.0206	$846.01	$846.00	$846.20