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	$113.67	13.390%	$128.8904	$128.89	$128.90	$128.90
Purchase #2	$111.91	10.687%	$123.8698	$123.87	$123.85	$123.90
Purchase #3	$199.61	10.166%	$219.9024	$219.90	$219.90	$219.90
Purchase #4	$36.55	5.457%	$38.5445	$38.54	$38.55	$38.50
Purchase #5	$100.82	12.550%	$113.4729	$113.47	$113.45	$113.50
Purchase #6	$226.45	10.796%	$250.8975	$250.90	$250.90	$250.90
Purchase #7	$249.41	10.659%	$275.9946	$275.99	$276.00	$276.00
7 purchase totals =	$1,038.42		$1,151.5721	$1,151.56	$1,151.55	$1,151.60