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	$99.51	13.301%	$112.7458	$112.75	$112.75	$112.70
Purchase #2	$244.93	8.422%	$265.558	$265.56	$265.55	$265.60
Purchase #3	$83.38	3.765%	$86.5193	$86.52	$86.50	$86.50
Purchase #4	$200.86	4.167%	$209.2298	$209.23	$209.25	$209.20
Purchase #5	$188.48	6.162%	$200.0941	$200.09	$200.10	$200.10
Purchase #6	$73.83	4.539%	$77.1811	$77.18	$77.20	$77.20
Purchase #7	$249.62	6.372%	$265.5258	$265.53	$265.55	$265.50
7 purchase totals =	$1,140.61		$1,216.8539	$1,216.86	$1,216.90	$1,216.80