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	$29.94	4.358%	$31.2448	$31.24	$31.25	$31.20
Purchase #2	$73.27	13.167%	$82.9175	$82.92	$82.90	$82.90
Purchase #3	$105.28	10.549%	$116.386	$116.39	$116.40	$116.40
Purchase #4	$103.70	12.402%	$116.5609	$116.56	$116.55	$116.60
Purchase #5	$39.85	6.481%	$42.4327	$42.43	$42.45	$42.40
Purchase #6	$193.78	7.545%	$208.4007	$208.40	$208.40	$208.40
Purchase #7	$201.44	7.291%	$216.127	$216.13	$216.15	$216.10
7 purchase totals =	$747.26		$814.0696	$814.07	$814.10	$814.00