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	$55.44	11.628%	$61.8866	$61.89	$61.90	$61.90
Purchase #2	$137.38	9.217%	$150.0423	$150.04	$150.05	$150.00
Purchase #3	$126.86	4.529%	$132.6055	$132.61	$132.60	$132.60
Purchase #4	$89.37	13.708%	$101.6208	$101.62	$101.60	$101.60
Purchase #5	$80.54	7.605%	$86.6651	$86.67	$86.65	$86.70
Purchase #6	$69.95	5.501%	$73.7979	$73.80	$73.80	$73.80
Purchase #7	$29.95	9.620%	$32.8312	$32.83	$32.85	$32.80
7 purchase totals =	$589.49		$639.4494	$639.46	$639.45	$639.40