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	$135.56	5.660%	$143.2327	$143.23	$143.25	$143.20
Purchase #2	$128.87	10.478%	$142.373	$142.37	$142.35	$142.40
Purchase #3	$182.38	5.530%	$192.4656	$192.47	$192.45	$192.50
Purchase #4	$55.90	4.561%	$58.4496	$58.45	$58.45	$58.40
Purchase #5	$133.58	12.686%	$150.526	$150.53	$150.55	$150.50
Purchase #6	$27.93	12.712%	$31.4805	$31.48	$31.50	$31.50
Purchase #7	$163.41	9.557%	$179.0271	$179.03	$179.05	$179.00
7 purchase totals =	$827.63		$897.5545	$897.56	$897.60	$897.50