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	$62.74	7.755%	$67.6055	$67.61	$67.60	$67.60
Purchase #2	$124.35	12.279%	$139.6189	$139.62	$139.60	$139.60
Purchase #3	$17.47	13.611%	$19.8478	$19.85	$19.85	$19.80
Purchase #4	$66.27	10.759%	$73.4	$73.40	$73.40	$73.40
Purchase #5	$25.55	7.619%	$27.4967	$27.50	$27.50	$27.50
Purchase #6	$172.64	9.279%	$188.6593	$188.66	$188.65	$188.70
Purchase #7	$82.51	4.691%	$86.3805	$86.38	$86.40	$86.40
7 purchase totals =	$551.53		$603.0087	$603.02	$603.00	$603.00