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	$19.80	10.361%	$21.8515	$21.85	$21.85	$21.90
Purchase #2	$196.26	6.392%	$208.8049	$208.80	$208.80	$208.80
Purchase #3	$11.84	13.209%	$13.4039	$13.40	$13.40	$13.40
Purchase #4	$171.46	5.863%	$181.5127	$181.51	$181.50	$181.50
Purchase #5	$132.48	5.804%	$140.1691	$140.17	$140.15	$140.20
Purchase #6	$37.34	13.866%	$42.5176	$42.52	$42.50	$42.50
Purchase #7	$56.98	11.197%	$63.3601	$63.36	$63.35	$63.40
7 purchase totals =	$626.16		$671.6198	$671.61	$671.55	$671.70