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	$31.95	10.224%	$35.2166	$35.22	$35.20	$35.20
Purchase #2	$200.77	4.830%	$210.4672	$210.47	$210.45	$210.50
Purchase #3	$229.47	11.463%	$255.7741	$255.77	$255.75	$255.80
Purchase #4	$74.83	7.185%	$80.2065	$80.21	$80.20	$80.20
Purchase #5	$143.25	3.746%	$148.6161	$148.62	$148.60	$148.60
Purchase #6	$153.85	7.579%	$165.5103	$165.51	$165.50	$165.50
Purchase #7	$218.92	11.581%	$244.2731	$244.27	$244.25	$244.30
7 purchase totals =	$1,053.04		$1,140.0639	$1,140.07	$1,139.95	$1,140.10