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	$97.80	7.690%	$105.3208	$105.32	$105.30	$105.30
Purchase #2	$232.90	13.790%	$265.0169	$265.02	$265.00	$265.00
Purchase #3	$224.90	13.571%	$255.4212	$255.42	$255.40	$255.40
Purchase #4	$67.99	6.678%	$72.5304	$72.53	$72.55	$72.50
Purchase #5	$78.37	3.823%	$81.3661	$81.37	$81.35	$81.40
Purchase #6	$122.72	13.772%	$139.621	$139.62	$139.60	$139.60
Purchase #7	$206.84	8.677%	$224.7875	$224.79	$224.80	$224.80
7 purchase totals =	$1,031.52		$1,144.0639	$1,144.07	$1,144.00	$1,144.00