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	$75.77	3.198%	$78.1931	$78.19	$78.20	$78.20
Purchase #2	$93.43	6.167%	$99.1918	$99.19	$99.20	$99.20
Purchase #3	$137.94	5.439%	$145.4426	$145.44	$145.45	$145.40
Purchase #4	$248.27	9.667%	$272.2703	$272.27	$272.25	$272.30
Purchase #5	$232.80	8.198%	$251.8849	$251.88	$251.90	$251.90
Purchase #6	$185.30	7.767%	$199.6923	$199.69	$199.70	$199.70
Purchase #7	$242.93	12.602%	$273.544	$273.54	$273.55	$273.50
7 purchase totals =	$1,216.44		$1,320.2190	$1,320.20	$1,320.25	$1,320.20