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	$17.82	11.648%	$19.8957	$19.90	$19.90	$19.90
Purchase #2	$195.93	12.537%	$220.4937	$220.49	$220.50	$220.50
Purchase #3	$52.28	3.725%	$54.2274	$54.23	$54.25	$54.20
Purchase #4	$207.38	12.108%	$232.4896	$232.49	$232.50	$232.50
Purchase #5	$33.89	10.487%	$37.444	$37.44	$37.45	$37.40
Purchase #6	$173.84	10.211%	$191.5908	$191.59	$191.60	$191.60
Purchase #7	$67.58	7.754%	$72.8202	$72.82	$72.80	$72.80
7 purchase totals =	$748.72		$828.9614	$828.96	$829.00	$828.90