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	$243.53	12.688%	$274.4291	$274.43	$274.45	$274.40
Purchase #2	$150.34	11.407%	$167.4893	$167.49	$167.50	$167.50
Purchase #3	$83.56	7.472%	$89.8036	$89.80	$89.80	$89.80
Purchase #4	$146.66	5.686%	$154.9991	$155.00	$155.00	$155.00
Purchase #5	$15.25	13.239%	$17.2689	$17.27	$17.25	$17.30
Purchase #6	$18.94	13.430%	$21.4836	$21.48	$21.50	$21.50
Purchase #7	$76.44	6.659%	$81.5301	$81.53	$81.55	$81.50
7 purchase totals =	$734.72		$807.0037	$807.00	$807.05	$807.00