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	$97.83	8.837%	$106.4752	$106.48	$106.50	$106.50
Purchase #2	$141.38	3.334%	$146.0936	$146.09	$146.10	$146.10
Purchase #3	$38.60	6.347%	$41.0499	$41.05	$41.05	$41.00
Purchase #4	$73.37	12.351%	$82.4319	$82.43	$82.45	$82.40
Purchase #5	$155.42	10.458%	$171.6738	$171.67	$171.65	$171.70
Purchase #6	$194.93	13.811%	$221.8518	$221.85	$221.85	$221.90
Purchase #7	$99.36	5.566%	$104.8904	$104.89	$104.90	$104.90
7 purchase totals =	$800.89		$874.4666	$874.46	$874.50	$874.50