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	$39.36	3.739%	$40.8317	$40.83	$40.85	$40.80
Purchase #2	$72.86	7.741%	$78.5001	$78.50	$78.50	$78.50
Purchase #3	$226.84	9.233%	$247.7841	$247.78	$247.80	$247.80
Purchase #4	$175.48	13.246%	$198.7241	$198.72	$198.70	$198.70
Purchase #5	$123.66	6.541%	$131.7486	$131.75	$131.75	$131.70
Purchase #6	$109.87	6.606%	$117.128	$117.13	$117.15	$117.10
Purchase #7	$212.55	10.316%	$234.4767	$234.48	$234.50	$234.50
7 purchase totals =	$960.62		$1,049.1933	$1,049.19	$1,049.25	$1,049.10