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	$84.67	7.345%	$90.889	$90.89	$90.90	$90.90
Purchase #2	$174.38	11.864%	$195.0684	$195.07	$195.05	$195.10
Purchase #3	$223.47	10.341%	$246.579	$246.58	$246.60	$246.60
Purchase #4	$112.69	6.611%	$120.1399	$120.14	$120.15	$120.10
Purchase #5	$100.59	7.184%	$107.8164	$107.82	$107.80	$107.80
Purchase #6	$39.85	6.621%	$42.4885	$42.49	$42.50	$42.50
Purchase #7	$30.56	8.497%	$33.1567	$33.16	$33.15	$33.20
7 purchase totals =	$766.21		$836.1379	$836.15	$836.15	$836.20