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	$117.98	11.232%	$131.2315	$131.23	$131.25	$131.20
Purchase #2	$128.71	8.611%	$139.7932	$139.79	$139.80	$139.80
Purchase #3	$145.98	13.319%	$165.4231	$165.42	$165.40	$165.40
Purchase #4	$154.25	10.137%	$169.8863	$169.89	$169.90	$169.90
Purchase #5	$240.53	11.249%	$267.5872	$267.59	$267.60	$267.60
Purchase #6	$190.89	9.479%	$208.9845	$208.98	$209.00	$209.00
Purchase #7	$133.88	8.232%	$144.901	$144.90	$144.90	$144.90
7 purchase totals =	$1,112.22		$1,227.8068	$1,227.80	$1,227.85	$1,227.80