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	$26.93	4.164%	$28.0514	$28.05	$28.05	$28.10
Purchase #2	$214.86	13.200%	$243.2215	$243.22	$243.20	$243.20
Purchase #3	$140.35	3.229%	$144.8819	$144.88	$144.90	$144.90
Purchase #4	$19.91	6.503%	$21.2047	$21.20	$21.20	$21.20
Purchase #5	$123.32	13.156%	$139.544	$139.54	$139.55	$139.50
Purchase #6	$69.85	11.756%	$78.0616	$78.06	$78.05	$78.10
Purchase #7	$27.28	9.842%	$29.9649	$29.96	$29.95	$30.00
7 purchase totals =	$622.50		$684.9300	$684.91	$684.90	$685.00