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	$64.45	11.678%	$71.9765	$71.98	$72.00	$72.00
Purchase #2	$217.68	9.598%	$238.5729	$238.57	$238.55	$238.60
Purchase #3	$209.35	5.511%	$220.8873	$220.89	$220.90	$220.90
Purchase #4	$78.88	10.660%	$87.2886	$87.29	$87.30	$87.30
Purchase #5	$17.76	9.517%	$19.4502	$19.45	$19.45	$19.50
Purchase #6	$62.64	5.864%	$66.3132	$66.31	$66.30	$66.30
Purchase #7	$42.80	7.225%	$45.8923	$45.89	$45.90	$45.90
7 purchase totals =	$693.56		$750.3810	$750.38	$750.40	$750.50