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	$246.72	7.297%	$264.7232	$264.72	$264.70	$264.70
Purchase #2	$101.61	10.770%	$112.5534	$112.55	$112.55	$112.60
Purchase #3	$116.31	8.804%	$126.5499	$126.55	$126.55	$126.50
Purchase #4	$87.48	12.564%	$98.471	$98.47	$98.45	$98.50
Purchase #5	$16.65	5.164%	$17.5098	$17.51	$17.50	$17.50
Purchase #6	$224.41	3.334%	$231.8918	$231.89	$231.90	$231.90
Purchase #7	$69.74	4.418%	$72.8211	$72.82	$72.80	$72.80
7 purchase totals =	$862.92		$924.5202	$924.51	$924.45	$924.50