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	$83.72	7.238%	$89.7797	$89.78	$89.80	$89.80
Purchase #2	$213.82	13.614%	$242.9295	$242.93	$242.95	$242.90
Purchase #3	$177.26	6.274%	$188.3813	$188.38	$188.40	$188.40
Purchase #4	$240.30	10.500%	$265.5315	$265.53	$265.55	$265.50
Purchase #5	$91.26	9.507%	$99.9361	$99.94	$99.95	$99.90
Purchase #6	$198.25	10.422%	$218.9116	$218.91	$218.90	$218.90
Purchase #7	$243.48	3.433%	$251.8387	$251.84	$251.85	$251.80
7 purchase totals =	$1,248.09		$1,357.3084	$1,357.31	$1,357.40	$1,357.20