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	$10.96	11.396%	$12.209	$12.21	$12.20	$12.20
Purchase #2	$113.46	3.568%	$117.5083	$117.51	$117.50	$117.50
Purchase #3	$206.35	9.493%	$225.9388	$225.94	$225.95	$225.90
Purchase #4	$34.48	12.707%	$38.8614	$38.86	$38.85	$38.90
Purchase #5	$71.86	11.688%	$80.259	$80.26	$80.25	$80.30
Purchase #6	$58.83	11.820%	$65.7837	$65.78	$65.80	$65.80
Purchase #7	$109.36	13.803%	$124.455	$124.46	$124.45	$124.50
7 purchase totals =	$605.30		$665.0152	$665.02	$665.00	$665.10