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	$150.90	10.490%	$166.7294	$166.73	$166.75	$166.70
Purchase #2	$40.68	4.236%	$42.4032	$42.40	$42.40	$42.40
Purchase #3	$93.95	10.427%	$103.7462	$103.75	$103.75	$103.70
Purchase #4	$190.27	8.590%	$206.6142	$206.61	$206.60	$206.60
Purchase #5	$38.57	11.351%	$42.9481	$42.95	$42.95	$42.90
Purchase #6	$39.98	9.683%	$43.8513	$43.85	$43.85	$43.90
Purchase #7	$6.57	13.599%	$7.4635	$7.46	$7.45	$7.50
7 purchase totals =	$560.92		$613.7559	$613.75	$613.75	$613.70