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	$48.98	12.759%	$55.2294	$55.23	$55.25	$55.20
Purchase #2	$43.85	12.258%	$49.2251	$49.23	$49.25	$49.20
Purchase #3	$179.37	4.832%	$188.0372	$188.04	$188.05	$188.00
Purchase #4	$186.95	9.752%	$205.1814	$205.18	$205.20	$205.20
Purchase #5	$73.71	5.561%	$77.809	$77.81	$77.80	$77.80
Purchase #6	$88.39	13.802%	$100.5896	$100.59	$100.60	$100.60
Purchase #7	$32.66	13.781%	$37.1609	$37.16	$37.15	$37.20
7 purchase totals =	$653.91		$713.2326	$713.24	$713.30	$713.20