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	$66.63	8.557%	$72.3315	$72.33	$72.35	$72.30
Purchase #2	$117.94	10.268%	$130.0501	$130.05	$130.05	$130.10
Purchase #3	$88.58	13.175%	$100.2504	$100.25	$100.25	$100.30
Purchase #4	$136.89	5.375%	$144.2478	$144.25	$144.25	$144.20
Purchase #5	$225.39	6.873%	$240.8811	$240.88	$240.90	$240.90
Purchase #6	$113.80	6.141%	$120.7885	$120.79	$120.80	$120.80
Purchase #7	$163.67	5.238%	$172.243	$172.24	$172.25	$172.20
7 purchase totals =	$912.90		$980.7924	$980.79	$980.85	$980.80