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	$133.47	6.469%	$142.1042	$142.10	$142.10	$142.10
Purchase #2	$71.91	6.332%	$76.4633	$76.46	$76.45	$76.50
Purchase #3	$51.81	6.218%	$55.0315	$55.03	$55.05	$55.00
Purchase #4	$140.70	7.546%	$151.3172	$151.32	$151.30	$151.30
Purchase #5	$37.96	13.865%	$43.2232	$43.22	$43.20	$43.20
Purchase #6	$87.47	6.154%	$92.8529	$92.85	$92.85	$92.90
Purchase #7	$117.63	8.387%	$127.4956	$127.50	$127.50	$127.50
7 purchase totals =	$640.95		$688.4879	$688.48	$688.45	$688.50