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	$57.49	3.501%	$59.5027	$59.50	$59.50	$59.50
Purchase #2	$205.93	8.576%	$223.5906	$223.59	$223.60	$223.60
Purchase #3	$227.89	10.279%	$251.3148	$251.31	$251.30	$251.30
Purchase #4	$187.83	13.683%	$213.5308	$213.53	$213.55	$213.50
Purchase #5	$139.79	13.424%	$158.5554	$158.56	$158.55	$158.60
Purchase #6	$109.29	10.691%	$120.9742	$120.97	$120.95	$121.00
Purchase #7	$246.70	4.688%	$258.2653	$258.27	$258.25	$258.30
7 purchase totals =	$1,174.92		$1,285.7338	$1,285.73	$1,285.70	$1,285.80