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	$218.87	3.618%	$226.7887	$226.79	$226.80	$226.80
Purchase #2	$55.33	7.500%	$59.4798	$59.48	$59.50	$59.50
Purchase #3	$227.87	5.436%	$240.257	$240.26	$240.25	$240.30
Purchase #4	$50.49	9.360%	$55.2159	$55.22	$55.20	$55.20
Purchase #5	$60.80	7.651%	$65.4518	$65.45	$65.45	$65.50
Purchase #6	$184.37	7.659%	$198.4909	$198.49	$198.50	$198.50
Purchase #7	$123.96	12.617%	$139.6	$139.60	$139.60	$139.60
7 purchase totals =	$921.69		$985.2841	$985.29	$985.30	$985.40