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	$27.51	13.146%	$31.1265	$31.13	$31.15	$31.10
Purchase #2	$141.45	10.484%	$156.2796	$156.28	$156.30	$156.30
Purchase #3	$105.30	10.264%	$116.108	$116.11	$116.10	$116.10
Purchase #4	$145.42	7.492%	$156.3149	$156.31	$156.30	$156.30
Purchase #5	$100.38	11.528%	$111.9518	$111.95	$111.95	$112.00
Purchase #6	$9.90	8.505%	$10.742	$10.74	$10.75	$10.70
Purchase #7	$207.93	6.252%	$220.9298	$220.93	$220.95	$220.90
7 purchase totals =	$737.89		$803.4526	$803.45	$803.50	$803.40