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	$188.88	9.549%	$206.9162	$206.92	$206.90	$206.90
Purchase #2	$227.31	12.619%	$255.9942	$255.99	$256.00	$256.00
Purchase #3	$228.82	9.387%	$250.2993	$250.30	$250.30	$250.30
Purchase #4	$108.48	3.671%	$112.4623	$112.46	$112.45	$112.50
Purchase #5	$138.74	10.188%	$152.8748	$152.87	$152.85	$152.90
Purchase #6	$231.66	13.308%	$262.4893	$262.49	$262.50	$262.50
Purchase #7	$148.75	12.165%	$166.8454	$166.85	$166.85	$166.80
7 purchase totals =	$1,272.64		$1,407.8815	$1,407.88	$1,407.85	$1,407.90