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	$5.44	7.600%	$5.8534	$5.85	$5.85	$5.90
Purchase #2	$61.51	7.724%	$66.261	$66.26	$66.25	$66.30
Purchase #3	$129.43	11.808%	$144.7131	$144.71	$144.70	$144.70
Purchase #4	$100.72	12.706%	$113.5175	$113.52	$113.50	$113.50
Purchase #5	$54.80	8.791%	$59.6175	$59.62	$59.60	$59.60
Purchase #6	$152.31	8.263%	$164.8954	$164.90	$164.90	$164.90
Purchase #7	$94.97	6.440%	$101.0861	$101.09	$101.10	$101.10
7 purchase totals =	$599.18		$655.9440	$655.95	$655.90	$656.00