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	$50.61	9.452%	$55.3937	$55.39	$55.40	$55.40
Purchase #2	$36.89	7.385%	$39.6143	$39.61	$39.60	$39.60
Purchase #3	$163.63	8.807%	$178.0409	$178.04	$178.05	$178.00
Purchase #4	$248.31	12.563%	$279.5052	$279.51	$279.50	$279.50
Purchase #5	$201.52	12.635%	$226.9821	$226.98	$227.00	$227.00
Purchase #6	$75.40	4.269%	$78.6188	$78.62	$78.60	$78.60
Purchase #7	$116.57	9.126%	$127.2082	$127.21	$127.20	$127.20
7 purchase totals =	$892.93		$985.3632	$985.36	$985.35	$985.30