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	$18.93	10.214%	$20.8635	$20.86	$20.85	$20.90
Purchase #2	$147.83	12.231%	$165.9111	$165.91	$165.90	$165.90
Purchase #3	$25.32	3.371%	$26.1735	$26.17	$26.15	$26.20
Purchase #4	$11.80	9.845%	$12.9617	$12.96	$12.95	$13.00
Purchase #5	$170.75	10.219%	$188.1989	$188.20	$188.20	$188.20
Purchase #6	$84.25	7.792%	$90.8148	$90.81	$90.80	$90.80
Purchase #7	$7.51	5.229%	$7.9027	$7.90	$7.90	$7.90
7 purchase totals =	$466.39		$512.8262	$512.81	$512.75	$512.90