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	$127.94	9.123%	$139.612	$139.61	$139.60	$139.60
Purchase #2	$97.65	7.661%	$105.131	$105.13	$105.15	$105.10
Purchase #3	$250.53	7.742%	$269.926	$269.93	$269.95	$269.90
Purchase #4	$217.82	13.307%	$246.8053	$246.81	$246.80	$246.80
Purchase #5	$78.32	8.659%	$85.1017	$85.10	$85.10	$85.10
Purchase #6	$50.26	5.216%	$52.8816	$52.88	$52.90	$52.90
Purchase #7	$90.34	8.539%	$98.0541	$98.05	$98.05	$98.10
7 purchase totals =	$912.86		$997.5117	$997.51	$997.55	$997.50