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 $56.87   8.423%   $61.6602   $61.66   $61.65   $61.70  
  Purchase #2 $92.29   13.423%   $104.6781   $104.68   $104.70   $104.70  
  Purchase #3 $55.31   8.824%   $60.1906   $60.19   $60.20   $60.20  
  Purchase #4 $242.87   3.212%   $250.671   $250.67   $250.65   $250.70  
  Purchase #5 $91.48   4.862%   $95.9278   $95.93   $95.95   $95.90  
  Purchase #6 $131.43   5.815%   $139.0727   $139.07   $139.05   $139.10  
  Purchase #7 $209.40   7.456%   $225.0129   $225.01   $225.00   $225.00  
  7 purchase totals = $879.65       $937.2133   $937.21   $937.20   $937.30