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	$40.31	4.193%	$42.0002	$42.00	$42.00	$42.00
Purchase #2	$84.83	4.858%	$88.951	$88.95	$88.95	$89.00
Purchase #3	$158.32	10.793%	$175.4075	$175.41	$175.40	$175.40
Purchase #4	$47.64	5.365%	$50.1959	$50.20	$50.20	$50.20
Purchase #5	$140.80	8.247%	$152.4118	$152.41	$152.40	$152.40
Purchase #6	$59.42	9.761%	$65.22	$65.22	$65.20	$65.20
Purchase #7	$170.97	11.372%	$190.4127	$190.41	$190.40	$190.40
7 purchase totals =	$702.29		$764.5991	$764.60	$764.55	$764.60