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 $198.49   3.674%   $205.7825   $205.78   $205.80   $205.80  
  Purchase #2 $66.88   5.779%   $70.745   $70.75   $70.75   $70.70  
  Purchase #3 $156.77   8.182%   $169.5969   $169.60   $169.60   $169.60  
  Purchase #4 $235.80   9.309%   $257.7506   $257.75   $257.75   $257.80  
  Purchase #5 $155.80   9.398%   $170.4421   $170.44   $170.45   $170.40  
  Purchase #6 $76.88   5.441%   $81.063   $81.06   $81.05   $81.10  
  Purchase #7 $141.92   10.141%   $156.3121   $156.31   $156.30   $156.30  
  7 purchase totals = $1,032.54       $1,111.6922   $1,111.69   $1,111.70   $1,111.70