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	$24.82	9.189%	$27.1007	$27.10	$27.10	$27.10
Purchase #2	$28.39	8.175%	$30.7109	$30.71	$30.70	$30.70
Purchase #3	$31.63	6.244%	$33.605	$33.61	$33.60	$33.60
Purchase #4	$59.76	4.387%	$62.3817	$62.38	$62.40	$62.40
Purchase #5	$76.26	5.386%	$80.3674	$80.37	$80.35	$80.40
Purchase #6	$29.98	11.229%	$33.3465	$33.35	$33.35	$33.30
Purchase #7	$64.67	12.759%	$72.9212	$72.92	$72.90	$72.90
7 purchase totals =	$315.51		$340.4334	$340.44	$340.40	$340.40