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	$47.27	12.755%	$53.2993	$53.30	$53.30	$53.30
Purchase #2	$242.44	3.439%	$250.7775	$250.78	$250.80	$250.80
Purchase #3	$84.78	12.164%	$95.0926	$95.09	$95.10	$95.10
Purchase #4	$117.58	8.571%	$127.6578	$127.66	$127.65	$127.70
Purchase #5	$226.83	13.845%	$258.2346	$258.23	$258.25	$258.20
Purchase #6	$250.67	13.660%	$284.9115	$284.91	$284.90	$284.90
Purchase #7	$195.89	12.277%	$219.9394	$219.94	$219.95	$219.90
7 purchase totals =	$1,165.46		$1,289.9127	$1,289.91	$1,289.95	$1,289.90