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 $76.92   7.313%   $82.5452   $82.55   $82.55   $82.50  
  Purchase #2 $227.36   5.736%   $240.4014   $240.40   $240.40   $240.40  
  Purchase #3 $156.81   6.827%   $167.5154   $167.52   $167.50   $167.50  
  Purchase #4 $188.49   9.611%   $206.6058   $206.61   $206.60   $206.60  
  Purchase #5 $75.58   8.638%   $82.1086   $82.11   $82.10   $82.10  
  Purchase #6 $65.74   12.616%   $74.0338   $74.03   $74.05   $74.00  
  Purchase #7 $40.37   11.151%   $44.8717   $44.87   $44.85   $44.90  
  7 purchase totals = $831.27       $898.0819   $898.09   $898.05   $898.00