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	$204.28	8.452%	$221.5457	$221.55	$221.55	$221.50
Purchase #2	$154.44	11.532%	$172.25	$172.25	$172.25	$172.30
Purchase #3	$126.86	7.465%	$136.3301	$136.33	$136.35	$136.30
Purchase #4	$145.89	13.230%	$165.1912	$165.19	$165.20	$165.20
Purchase #5	$47.75	3.808%	$49.5683	$49.57	$49.55	$49.60
Purchase #6	$111.25	10.165%	$122.5586	$122.56	$122.55	$122.60
Purchase #7	$165.70	4.131%	$172.5451	$172.55	$172.55	$172.50
7 purchase totals =	$956.17		$1,039.9890	$1,040.00	$1,040.00	$1,040.00