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	$51.78	11.798%	$57.889	$57.89	$57.90	$57.90
Purchase #2	$34.57	4.226%	$36.0309	$36.03	$36.05	$36.00
Purchase #3	$100.56	4.240%	$104.8237	$104.82	$104.80	$104.80
Purchase #4	$63.35	9.697%	$69.493	$69.49	$69.50	$69.50
Purchase #5	$206.76	6.297%	$219.7797	$219.78	$219.80	$219.80
Purchase #6	$11.98	4.422%	$12.5098	$12.51	$12.50	$12.50
Purchase #7	$180.61	5.148%	$189.9078	$189.91	$189.90	$189.90
7 purchase totals =	$649.61		$690.4339	$690.43	$690.45	$690.40