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	$69.58	12.583%	$78.3353	$78.34	$78.35	$78.30
Purchase #2	$57.85	7.690%	$62.2987	$62.30	$62.30	$62.30
Purchase #3	$219.56	9.667%	$240.7849	$240.78	$240.80	$240.80
Purchase #4	$123.86	4.682%	$129.6591	$129.66	$129.65	$129.70
Purchase #5	$25.73	12.155%	$28.8575	$28.86	$28.85	$28.90
Purchase #6	$65.30	10.868%	$72.3968	$72.40	$72.40	$72.40
Purchase #7	$234.61	9.189%	$256.1683	$256.17	$256.15	$256.20
7 purchase totals =	$796.49		$868.5006	$868.51	$868.50	$868.60