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	$35.96	12.181%	$40.3403	$40.34	$40.35	$40.30
Purchase #2	$186.45	9.338%	$203.8607	$203.86	$203.85	$203.90
Purchase #3	$158.38	5.386%	$166.9103	$166.91	$166.90	$166.90
Purchase #4	$38.82	10.131%	$42.7529	$42.75	$42.75	$42.80
Purchase #5	$154.53	8.433%	$167.5615	$167.56	$167.55	$167.60
Purchase #6	$61.28	3.590%	$63.48	$63.48	$63.50	$63.50
Purchase #7	$225.36	3.871%	$234.0837	$234.08	$234.10	$234.10
7 purchase totals =	$860.78		$918.9894	$918.98	$919.00	$919.10