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	$41.49	6.420%	$44.1537	$44.15	$44.15	$44.20
Purchase #2	$225.97	10.675%	$250.0923	$250.09	$250.10	$250.10
Purchase #3	$131.36	6.119%	$139.3979	$139.40	$139.40	$139.40
Purchase #4	$59.72	7.553%	$64.2307	$64.23	$64.25	$64.20
Purchase #5	$228.39	12.153%	$256.1462	$256.15	$256.15	$256.10
Purchase #6	$12.80	8.371%	$13.8715	$13.87	$13.85	$13.90
Purchase #7	$160.90	3.481%	$166.5009	$166.50	$166.50	$166.50
7 purchase totals =	$860.63		$934.3932	$934.39	$934.40	$934.40