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	$173.26	6.541%	$184.5929	$184.59	$184.60	$184.60
Purchase #2	$65.96	6.161%	$70.0238	$70.02	$70.00	$70.00
Purchase #3	$250.91	3.460%	$259.5915	$259.59	$259.60	$259.60
Purchase #4	$67.79	12.140%	$76.0197	$76.02	$76.00	$76.00
Purchase #5	$131.91	8.868%	$143.6078	$143.61	$143.60	$143.60
Purchase #6	$53.31	10.687%	$59.0072	$59.01	$59.00	$59.00
Purchase #7	$136.51	3.698%	$141.5581	$141.56	$141.55	$141.60
7 purchase totals =	$879.65		$934.4010	$934.40	$934.35	$934.40