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	$231.48	9.520%	$253.5169	$253.52	$253.50	$253.50
Purchase #2	$206.64	12.514%	$232.4989	$232.50	$232.50	$232.50
Purchase #3	$40.64	10.293%	$44.8231	$44.82	$44.80	$44.80
Purchase #4	$43.56	4.471%	$45.5076	$45.51	$45.50	$45.50
Purchase #5	$15.39	7.678%	$16.5716	$16.57	$16.55	$16.60
Purchase #6	$140.80	8.408%	$152.6385	$152.64	$152.65	$152.60
Purchase #7	$224.54	3.809%	$233.0927	$233.09	$233.10	$233.10
7 purchase totals =	$903.05		$978.6493	$978.65	$978.60	$978.60