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	$49.62	13.274%	$56.2066	$56.21	$56.20	$56.20
Purchase #2	$121.65	8.140%	$131.5523	$131.55	$131.55	$131.60
Purchase #3	$234.80	11.859%	$262.6449	$262.64	$262.65	$262.60
Purchase #4	$45.54	10.846%	$50.4793	$50.48	$50.50	$50.50
Purchase #5	$96.69	6.436%	$102.913	$102.91	$102.90	$102.90
Purchase #6	$224.27	13.389%	$254.2975	$254.30	$254.30	$254.30
Purchase #7	$137.95	12.296%	$154.9123	$154.91	$154.90	$154.90
7 purchase totals =	$910.52		$1,013.0059	$1,013.00	$1,013.00	$1,013.00