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	$118.28	11.516%	$131.9011	$131.90	$131.90	$131.90
Purchase #2	$144.48	12.131%	$162.0069	$162.01	$162.00	$162.00
Purchase #3	$94.86	4.306%	$98.9447	$98.94	$98.95	$98.90
Purchase #4	$36.56	13.525%	$41.5047	$41.50	$41.50	$41.50
Purchase #5	$62.79	6.490%	$66.8651	$66.87	$66.85	$66.90
Purchase #6	$40.89	8.226%	$44.2536	$44.25	$44.25	$44.30
Purchase #7	$8.56	3.454%	$8.8557	$8.86	$8.85	$8.90
7 purchase totals =	$506.42		$554.3318	$554.33	$554.30	$554.40