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	$44.79	11.257%	$49.832	$49.83	$49.85	$49.80
Purchase #2	$183.29	11.249%	$203.9083	$203.91	$203.90	$203.90
Purchase #3	$143.66	9.366%	$157.1152	$157.12	$157.10	$157.10
Purchase #4	$48.59	6.179%	$51.5924	$51.59	$51.60	$51.60
Purchase #5	$151.91	8.623%	$165.0092	$165.01	$165.00	$165.00
Purchase #6	$70.53	11.787%	$78.8434	$78.84	$78.85	$78.80
Purchase #7	$37.82	7.363%	$40.6047	$40.60	$40.60	$40.60
7 purchase totals =	$680.59		$746.9052	$746.90	$746.90	$746.80