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 $142.67   13.639%   $162.1288   $162.13   $162.15   $162.10  
  Purchase #2 $242.26   9.407%   $265.0494   $265.05   $265.05   $265.00  
  Purchase #3 $24.36   6.421%   $25.9242   $25.92   $25.90   $25.90  
  Purchase #4 $78.93   6.581%   $84.1244   $84.12   $84.10   $84.10  
  Purchase #5 $100.69   4.641%   $105.363   $105.36   $105.35   $105.40  
  Purchase #6 $104.71   5.385%   $110.3486   $110.35   $110.35   $110.30  
  Purchase #7 $188.67   7.104%   $202.0731   $202.07   $202.05   $202.10  
  7 purchase totals = $882.29       $955.0115   $955.00   $954.95   $954.90