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	$68.97	6.216%	$73.2572	$73.26	$73.25	$73.30
Purchase #2	$18.73	10.342%	$20.6671	$20.67	$20.65	$20.70
Purchase #3	$206.34	8.492%	$223.8624	$223.86	$223.85	$223.90
Purchase #4	$121.69	4.249%	$126.8606	$126.86	$126.85	$126.90
Purchase #5	$113.43	8.604%	$123.1895	$123.19	$123.20	$123.20
Purchase #6	$79.52	13.638%	$90.3649	$90.36	$90.35	$90.40
Purchase #7	$198.78	12.659%	$223.9436	$223.94	$223.95	$223.90
7 purchase totals =	$807.46		$882.1453	$882.14	$882.10	$882.30