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 $30.44   13.838%   $34.6523   $34.65   $34.65   $34.70  
  Purchase #2 $177.71   5.732%   $187.8963   $187.90   $187.90   $187.90  
  Purchase #3 $78.31   6.173%   $83.1441   $83.14   $83.15   $83.10  
  Purchase #4 $95.32   13.284%   $107.9823   $107.98   $108.00   $108.00  
  Purchase #5 $207.76   6.154%   $220.5456   $220.55   $220.55   $220.50  
  Purchase #6 $62.30   8.697%   $67.7182   $67.72   $67.70   $67.70  
  Purchase #7 $239.37   5.547%   $252.6479   $252.65   $252.65   $252.60  
  7 purchase totals = $891.21       $954.5867   $954.59   $954.60   $954.50