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	$38.34	5.179%	$40.3256	$40.33	$40.35	$40.30
Purchase #2	$232.25	7.621%	$249.9498	$249.95	$249.95	$249.90
Purchase #3	$101.56	12.810%	$114.5698	$114.57	$114.55	$114.60
Purchase #4	$104.64	13.587%	$118.8574	$118.86	$118.85	$118.90
Purchase #5	$123.87	12.281%	$139.0825	$139.08	$139.10	$139.10
Purchase #6	$64.38	4.431%	$67.2327	$67.23	$67.25	$67.20
Purchase #7	$203.55	4.823%	$213.3672	$213.37	$213.35	$213.40
7 purchase totals =	$868.59		$943.3850	$943.39	$943.40	$943.40