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	$69.78	5.358%	$73.5188	$73.52	$73.50	$73.50
Purchase #2	$213.84	5.663%	$225.9498	$225.95	$225.95	$225.90
Purchase #3	$38.48	10.247%	$42.423	$42.42	$42.40	$42.40
Purchase #4	$43.57	5.601%	$46.0104	$46.01	$46.00	$46.00
Purchase #5	$28.80	12.248%	$32.3274	$32.33	$32.35	$32.30
Purchase #6	$43.34	5.699%	$45.8099	$45.81	$45.80	$45.80
Purchase #7	$162.35	4.570%	$169.7694	$169.77	$169.75	$169.80
7 purchase totals =	$600.16		$635.8087	$635.81	$635.75	$635.70