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	$37.54	12.825%	$42.3545	$42.35	$42.35	$42.40
Purchase #2	$30.89	8.228%	$33.4316	$33.43	$33.45	$33.40
Purchase #3	$66.33	9.137%	$72.3906	$72.39	$72.40	$72.40
Purchase #4	$199.77	13.184%	$226.1077	$226.11	$226.10	$226.10
Purchase #5	$44.27	12.304%	$49.717	$49.72	$49.70	$49.70
Purchase #6	$220.41	10.483%	$243.5156	$243.52	$243.50	$243.50
Purchase #7	$245.68	12.376%	$276.0854	$276.09	$276.10	$276.10
7 purchase totals =	$844.89		$943.6024	$943.61	$943.60	$943.60