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 $58.92   3.481%   $60.971   $60.97   $60.95   $61.00  
  Purchase #2 $250.69   8.429%   $271.8207   $271.82   $271.80   $271.80  
  Purchase #3 $174.66   13.787%   $198.7404   $198.74   $198.75   $198.70  
  Purchase #4 $65.25   3.270%   $67.3837   $67.38   $67.40   $67.40  
  Purchase #5 $28.55   7.506%   $30.693   $30.69   $30.70   $30.70  
  Purchase #6 $73.72   12.816%   $83.168   $83.17   $83.15   $83.20  
  Purchase #7 $122.59   4.721%   $128.3775   $128.38   $128.40   $128.40  
  7 purchase totals = $774.38       $841.1543   $841.15   $841.15   $841.20