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 $93.31   12.471%   $104.9467   $104.95   $104.95   $104.90  
  Purchase #2 $46.89   6.396%   $49.8891   $49.89   $49.90   $49.90  
  Purchase #3 $56.48   8.346%   $61.1938   $61.19   $61.20   $61.20  
  Purchase #4 $85.32   9.400%   $93.3401   $93.34   $93.35   $93.30  
  Purchase #5 $225.93   5.515%   $238.39   $238.39   $238.40   $238.40  
  Purchase #6 $43.43   7.476%   $46.6768   $46.68   $46.70   $46.70  
  Purchase #7 $102.28   3.317%   $105.6726   $105.67   $105.65   $105.70  
  7 purchase totals = $653.64       $700.1091   $700.11   $700.15   $700.10