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	$159.28	13.369%	$180.5741	$180.57	$180.55	$180.60
Purchase #2	$196.45	12.638%	$221.2774	$221.28	$221.30	$221.30
Purchase #3	$231.41	10.505%	$255.7196	$255.72	$255.70	$255.70
Purchase #4	$40.25	13.779%	$45.796	$45.80	$45.80	$45.80
Purchase #5	$50.77	4.107%	$52.8551	$52.86	$52.85	$52.90
Purchase #6	$51.86	8.640%	$56.3407	$56.34	$56.35	$56.30
Purchase #7	$110.75	11.343%	$123.3124	$123.31	$123.30	$123.30
7 purchase totals =	$840.77		$935.8753	$935.88	$935.85	$935.90