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	$50.76	13.386%	$57.5547	$57.55	$57.55	$57.60
Purchase #2	$111.32	13.401%	$126.238	$126.24	$126.25	$126.20
Purchase #3	$109.28	9.870%	$120.0659	$120.07	$120.05	$120.10
Purchase #4	$34.67	9.706%	$38.0351	$38.04	$38.05	$38.00
Purchase #5	$247.58	9.145%	$270.2212	$270.22	$270.20	$270.20
Purchase #6	$137.82	6.335%	$146.5509	$146.55	$146.55	$146.60
Purchase #7	$65.60	3.497%	$67.894	$67.89	$67.90	$67.90
7 purchase totals =	$757.03		$826.5598	$826.56	$826.55	$826.60