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	$64.88	11.580%	$72.3931	$72.39	$72.40	$72.40
Purchase #2	$163.79	11.533%	$182.6799	$182.68	$182.70	$182.70
Purchase #3	$217.42	5.277%	$228.8933	$228.89	$228.90	$228.90
Purchase #4	$105.55	7.161%	$113.1084	$113.11	$113.10	$113.10
Purchase #5	$155.44	11.174%	$172.8089	$172.81	$172.80	$172.80
Purchase #6	$37.83	12.488%	$42.5542	$42.55	$42.55	$42.60
Purchase #7	$40.77	13.369%	$46.2205	$46.22	$46.20	$46.20
7 purchase totals =	$785.68		$858.6583	$858.65	$858.65	$858.70