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	$41.72	9.834%	$45.8227	$45.82	$45.80	$45.80
Purchase #2	$239.93	4.359%	$250.3885	$250.39	$250.40	$250.40
Purchase #3	$73.34	4.849%	$76.8963	$76.90	$76.90	$76.90
Purchase #4	$228.29	4.339%	$238.1955	$238.20	$238.20	$238.20
Purchase #5	$78.77	5.820%	$83.3544	$83.35	$83.35	$83.40
Purchase #6	$129.69	7.505%	$139.4232	$139.42	$139.40	$139.40
Purchase #7	$33.92	10.326%	$37.4226	$37.42	$37.40	$37.40
7 purchase totals =	$825.66		$871.5032	$871.50	$871.45	$871.50