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	$73.59	9.590%	$80.6473	$80.65	$80.65	$80.60
Purchase #2	$177.57	12.555%	$199.8639	$199.86	$199.85	$199.90
Purchase #3	$248.51	10.747%	$275.2174	$275.22	$275.20	$275.20
Purchase #4	$224.31	13.533%	$254.6659	$254.67	$254.65	$254.70
Purchase #5	$40.71	11.824%	$45.5236	$45.52	$45.50	$45.50
Purchase #6	$50.47	4.462%	$52.722	$52.72	$52.70	$52.70
Purchase #7	$27.37	11.269%	$30.4543	$30.45	$30.45	$30.50
7 purchase totals =	$842.53		$939.0944	$939.09	$939.00	$939.10