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	$93.52	12.161%	$104.893	$104.89	$104.90	$104.90
Purchase #2	$214.73	5.767%	$227.1135	$227.11	$227.10	$227.10
Purchase #3	$198.44	3.610%	$205.6037	$205.60	$205.60	$205.60
Purchase #4	$11.69	11.343%	$13.016	$13.02	$13.00	$13.00
Purchase #5	$34.32	9.426%	$37.555	$37.56	$37.55	$37.60
Purchase #6	$18.59	8.551%	$20.1796	$20.18	$20.20	$20.20
Purchase #7	$198.60	12.188%	$222.8054	$222.81	$222.80	$222.80
7 purchase totals =	$769.89		$831.1662	$831.17	$831.15	$831.20