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 $62.83   3.658%   $65.1283   $65.13   $65.15   $65.10  
  Purchase #2 $238.49   4.322%   $248.7975   $248.80   $248.80   $248.80  
  Purchase #3 $9.63   8.266%   $10.426   $10.43   $10.45   $10.40  
  Purchase #4 $240.54   4.317%   $250.9241   $250.92   $250.90   $250.90  
  Purchase #5 $240.59   8.765%   $261.6777   $261.68   $261.70   $261.70  
  Purchase #6 $11.53   6.147%   $12.2387   $12.24   $12.25   $12.20  
  Purchase #7 $20.45   6.213%   $21.7206   $21.72   $21.70   $21.70  
  7 purchase totals = $824.06       $870.9129   $870.92   $870.95   $870.80