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	$116.57	10.266%	$128.5371	$128.54	$128.55	$128.50
Purchase #2	$188.50	13.341%	$213.6478	$213.65	$213.65	$213.60
Purchase #3	$116.27	3.577%	$120.429	$120.43	$120.45	$120.40
Purchase #4	$196.65	7.796%	$211.9808	$211.98	$212.00	$212.00
Purchase #5	$105.48	7.382%	$113.2665	$113.27	$113.25	$113.30
Purchase #6	$12.65	5.561%	$13.3535	$13.35	$13.35	$13.40
Purchase #7	$55.32	7.507%	$59.4729	$59.47	$59.45	$59.50
7 purchase totals =	$791.44		$860.6876	$860.69	$860.70	$860.70