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	$66.25	9.855%	$72.7789	$72.78	$72.80	$72.80
Purchase #2	$154.83	11.402%	$172.4837	$172.48	$172.50	$172.50
Purchase #3	$116.47	3.807%	$120.904	$120.90	$120.90	$120.90
Purchase #4	$148.57	11.448%	$165.5783	$165.58	$165.60	$165.60
Purchase #5	$21.63	11.213%	$24.0554	$24.06	$24.05	$24.10
Purchase #6	$219.80	8.532%	$238.5533	$238.55	$238.55	$238.60
Purchase #7	$143.35	6.320%	$152.4097	$152.41	$152.40	$152.40
7 purchase totals =	$870.90		$946.7633	$946.76	$946.80	$946.90