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	$19.60	4.111%	$20.4058	$20.41	$20.40	$20.40
Purchase #2	$143.80	4.673%	$150.5198	$150.52	$150.50	$150.50
Purchase #3	$199.33	11.401%	$222.0556	$222.06	$222.05	$222.10
Purchase #4	$218.35	4.675%	$228.5579	$228.56	$228.55	$228.60
Purchase #5	$243.86	13.839%	$277.6078	$277.61	$277.60	$277.60
Purchase #6	$13.64	5.547%	$14.3966	$14.40	$14.40	$14.40
Purchase #7	$104.57	12.377%	$117.5126	$117.51	$117.50	$117.50
7 purchase totals =	$943.15		$1,031.0561	$1,031.07	$1,031.00	$1,031.10