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	$144.81	13.602%	$164.5071	$164.51	$164.50	$164.50
Purchase #2	$68.77	3.485%	$71.1666	$71.17	$71.15	$71.20
Purchase #3	$77.88	9.234%	$85.0714	$85.07	$85.05	$85.10
Purchase #4	$91.92	10.185%	$101.2821	$101.28	$101.30	$101.30
Purchase #5	$241.77	3.410%	$250.0144	$250.01	$250.00	$250.00
Purchase #6	$26.45	10.594%	$29.2521	$29.25	$29.25	$29.30
Purchase #7	$121.72	7.235%	$130.5264	$130.53	$130.55	$130.50
7 purchase totals =	$773.32		$831.8201	$831.82	$831.80	$831.90