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	$59.78	11.464%	$66.6332	$66.63	$66.65	$66.60
Purchase #2	$37.35	10.173%	$41.1496	$41.15	$41.15	$41.10
Purchase #3	$104.37	8.701%	$113.4512	$113.45	$113.45	$113.50
Purchase #4	$65.64	9.143%	$71.6415	$71.64	$71.65	$71.60
Purchase #5	$126.88	4.814%	$132.988	$132.99	$133.00	$133.00
Purchase #6	$171.86	11.449%	$191.5363	$191.54	$191.55	$191.50
Purchase #7	$18.82	6.786%	$20.0971	$20.10	$20.10	$20.10
7 purchase totals =	$584.70		$637.4969	$637.50	$637.55	$637.40