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	$16.78	13.301%	$19.0119	$19.01	$19.00	$19.00
Purchase #2	$138.78	8.427%	$150.475	$150.48	$150.50	$150.50
Purchase #3	$35.90	5.351%	$37.821	$37.82	$37.80	$37.80
Purchase #4	$159.39	8.791%	$173.402	$173.40	$173.40	$173.40
Purchase #5	$225.53	3.548%	$233.5318	$233.53	$233.55	$233.50
Purchase #6	$63.83	12.788%	$71.9926	$71.99	$72.00	$72.00
Purchase #7	$26.48	10.153%	$29.1685	$29.17	$29.15	$29.20
7 purchase totals =	$666.69		$715.4028	$715.40	$715.40	$715.40