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	$241.59	5.805%	$255.6143	$255.61	$255.60	$255.60
Purchase #2	$122.67	7.232%	$131.5415	$131.54	$131.55	$131.50
Purchase #3	$29.52	3.383%	$30.5187	$30.52	$30.50	$30.50
Purchase #4	$184.78	7.557%	$198.7438	$198.74	$198.75	$198.70
Purchase #5	$212.48	11.736%	$237.4167	$237.42	$237.40	$237.40
Purchase #6	$59.76	12.322%	$67.1236	$67.12	$67.10	$67.10
Purchase #7	$31.30	11.290%	$34.8338	$34.83	$34.85	$34.80
7 purchase totals =	$882.10		$955.7924	$955.78	$955.75	$955.60