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	$140.90	12.596%	$158.6478	$158.65	$158.65	$158.60
Purchase #2	$192.87	10.674%	$213.4569	$213.46	$213.45	$213.50
Purchase #3	$120.93	5.723%	$127.8508	$127.85	$127.85	$127.90
Purchase #4	$35.78	4.603%	$37.427	$37.43	$37.45	$37.40
Purchase #5	$171.34	5.333%	$180.4776	$180.48	$180.50	$180.50
Purchase #6	$128.97	8.830%	$140.3581	$140.36	$140.35	$140.40
Purchase #7	$43.60	6.486%	$46.4279	$46.43	$46.45	$46.40
7 purchase totals =	$834.39		$904.6461	$904.66	$904.70	$904.70