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	$52.48	6.752%	$56.0234	$56.02	$56.00	$56.00
Purchase #2	$152.89	13.289%	$173.2076	$173.21	$173.20	$173.20
Purchase #3	$37.82	11.196%	$42.0543	$42.05	$42.05	$42.10
Purchase #4	$240.97	8.552%	$261.5778	$261.58	$261.60	$261.60
Purchase #5	$140.52	12.322%	$157.8349	$157.83	$157.85	$157.80
Purchase #6	$40.75	13.316%	$46.1763	$46.18	$46.20	$46.20
Purchase #7	$83.82	6.778%	$89.5013	$89.50	$89.50	$89.50
7 purchase totals =	$749.25		$826.3756	$826.37	$826.40	$826.40