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	$52.66	7.281%	$56.4942	$56.49	$56.50	$56.50
Purchase #2	$125.51	3.583%	$130.007	$130.01	$130.00	$130.00
Purchase #3	$66.97	10.338%	$73.8934	$73.89	$73.90	$73.90
Purchase #4	$10.63	11.812%	$11.8856	$11.89	$11.90	$11.90
Purchase #5	$70.84	11.124%	$78.7202	$78.72	$78.70	$78.70
Purchase #6	$48.79	11.200%	$54.2545	$54.25	$54.25	$54.30
Purchase #7	$225.93	12.131%	$253.3376	$253.34	$253.35	$253.30
7 purchase totals =	$601.33		$658.5925	$658.59	$658.60	$658.60