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 $248.56   5.180%   $261.4354   $261.44   $261.45   $261.40  
  Purchase #2 $20.65   9.718%   $22.6568   $22.66   $22.65   $22.70  
  Purchase #3 $77.94   13.154%   $88.1922   $88.19   $88.20   $88.20  
  Purchase #4 $166.27   4.865%   $174.359   $174.36   $174.35   $174.40  
  Purchase #5 $177.30   11.610%   $197.8845   $197.88   $197.90   $197.90  
  Purchase #6 $158.58   13.143%   $179.4222   $179.42   $179.40   $179.40  
  Purchase #7 $211.87   6.354%   $225.3322   $225.33   $225.35   $225.30  
  7 purchase totals = $1,061.17       $1,149.2823   $1,149.28   $1,149.30   $1,149.30