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	$92.26	7.822%	$99.4766	$99.48	$99.50	$99.50
Purchase #2	$84.40	4.166%	$87.9161	$87.92	$87.90	$87.90
Purchase #3	$150.28	13.643%	$170.7827	$170.78	$170.80	$170.80
Purchase #4	$50.91	12.754%	$57.4031	$57.40	$57.40	$57.40
Purchase #5	$114.30	7.827%	$123.2463	$123.25	$123.25	$123.20
Purchase #6	$57.31	9.755%	$62.9006	$62.90	$62.90	$62.90
Purchase #7	$18.94	6.736%	$20.2158	$20.22	$20.20	$20.20
7 purchase totals =	$568.40		$621.9412	$621.95	$621.95	$621.90