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 $91.63   13.654%   $104.1412   $104.14   $104.15   $104.10  
  Purchase #2 $40.48   7.870%   $43.6658   $43.67   $43.65   $43.70  
  Purchase #3 $76.69   13.322%   $86.9066   $86.91   $86.90   $86.90  
  Purchase #4 $175.64   4.161%   $182.9484   $182.95   $182.95   $182.90  
  Purchase #5 $246.98   8.593%   $268.203   $268.20   $268.20   $268.20  
  Purchase #6 $103.47   5.425%   $109.0832   $109.08   $109.10   $109.10  
  Purchase #7 $10.64   9.326%   $11.6323   $11.63   $11.65   $11.60  
  7 purchase totals = $745.53       $806.5805   $806.58   $806.60   $806.50