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	$37.39	12.810%	$42.1797	$42.18	$42.20	$42.20
Purchase #2	$10.34	13.306%	$11.7158	$11.72	$11.70	$11.70
Purchase #3	$123.53	6.139%	$131.1135	$131.11	$131.10	$131.10
Purchase #4	$137.64	9.160%	$150.2478	$150.25	$150.25	$150.20
Purchase #5	$69.31	10.804%	$76.7983	$76.80	$76.80	$76.80
Purchase #6	$93.74	6.758%	$100.0749	$100.07	$100.05	$100.10
Purchase #7	$168.63	4.157%	$175.6399	$175.64	$175.65	$175.60
7 purchase totals =	$640.58		$687.7699	$687.77	$687.75	$687.70