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 $48.69   10.761%   $53.9295   $53.93   $53.95   $53.90  
  Purchase #2 $121.55   10.328%   $134.1037   $134.10   $134.10   $134.10  
  Purchase #3 $51.75   6.617%   $55.1743   $55.17   $55.15   $55.20  
  Purchase #4 $211.56   7.161%   $226.7098   $226.71   $226.70   $226.70  
  Purchase #5 $36.69   13.637%   $41.6934   $41.69   $41.70   $41.70  
  Purchase #6 $22.49   8.697%   $24.446   $24.45   $24.45   $24.40  
  Purchase #7 $232.26   13.166%   $262.8394   $262.84   $262.85   $262.80  
  7 purchase totals = $724.99       $798.8961   $798.89   $798.90   $798.80