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	$204.82	5.703%	$216.5009	$216.50	$216.50	$216.50
Purchase #2	$37.81	12.243%	$42.4391	$42.44	$42.45	$42.40
Purchase #3	$106.55	10.671%	$117.92	$117.92	$117.90	$117.90
Purchase #4	$94.76	5.602%	$100.0685	$100.07	$100.05	$100.10
Purchase #5	$40.57	12.711%	$45.7269	$45.73	$45.75	$45.70
Purchase #6	$12.80	5.113%	$13.4545	$13.45	$13.45	$13.50
Purchase #7	$13.50	7.688%	$14.5379	$14.54	$14.55	$14.50
7 purchase totals =	$510.81		$550.6478	$550.65	$550.65	$550.60