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	$59.31	12.239%	$66.569	$66.57	$66.55	$66.60
Purchase #2	$40.36	12.402%	$45.3654	$45.37	$45.35	$45.40
Purchase #3	$63.80	5.859%	$67.538	$67.54	$67.55	$67.50
Purchase #4	$128.43	10.768%	$142.2593	$142.26	$142.25	$142.30
Purchase #5	$247.51	10.805%	$274.2535	$274.25	$274.25	$274.30
Purchase #6	$32.69	9.270%	$35.7204	$35.72	$35.70	$35.70
Purchase #7	$45.84	12.577%	$51.6053	$51.61	$51.60	$51.60
7 purchase totals =	$617.94		$683.3109	$683.32	$683.25	$683.40