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	$30.52	3.229%	$31.5055	$31.51	$31.50	$31.50
Purchase #2	$49.86	12.339%	$56.0122	$56.01	$56.00	$56.00
Purchase #3	$113.78	10.833%	$126.1058	$126.11	$126.10	$126.10
Purchase #4	$13.71	10.347%	$15.1286	$15.13	$15.15	$15.10
Purchase #5	$36.28	12.771%	$40.9133	$40.91	$40.90	$40.90
Purchase #6	$168.31	13.756%	$191.4627	$191.46	$191.45	$191.50
Purchase #7	$242.93	8.307%	$263.1102	$263.11	$263.10	$263.10
7 purchase totals =	$655.39		$724.2383	$724.24	$724.20	$724.20