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	$234.87	8.646%	$255.1769	$255.18	$255.20	$255.20
Purchase #2	$64.80	8.155%	$70.0844	$70.08	$70.10	$70.10
Purchase #3	$214.29	6.253%	$227.6896	$227.69	$227.70	$227.70
Purchase #4	$132.43	9.390%	$144.8652	$144.87	$144.85	$144.90
Purchase #5	$140.28	8.148%	$151.71	$151.71	$151.70	$151.70
Purchase #6	$123.31	13.438%	$139.8804	$139.88	$139.90	$139.90
Purchase #7	$237.91	3.181%	$245.4779	$245.48	$245.50	$245.50
7 purchase totals =	$1,147.89		$1,234.8844	$1,234.89	$1,234.95	$1,235.00