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	$31.63	8.698%	$34.3812	$34.38	$34.40	$34.40
Purchase #2	$101.88	9.648%	$111.7094	$111.71	$111.70	$111.70
Purchase #3	$77.93	9.768%	$85.5422	$85.54	$85.55	$85.50
Purchase #4	$178.61	5.383%	$188.2246	$188.22	$188.20	$188.20
Purchase #5	$133.31	4.610%	$139.4556	$139.46	$139.45	$139.50
Purchase #6	$64.89	11.658%	$72.4549	$72.45	$72.45	$72.50
Purchase #7	$195.64	5.795%	$206.9773	$206.98	$207.00	$207.00
7 purchase totals =	$783.89		$838.7452	$838.74	$838.75	$838.80