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 $62.71   11.130%   $69.6896   $69.69   $69.70   $69.70  
  Purchase #2 $157.48   5.532%   $166.1918   $166.19   $166.20   $166.20  
  Purchase #3 $130.76   4.715%   $136.9253   $136.93   $136.95   $136.90  
  Purchase #4 $19.43   6.526%   $20.698   $20.70   $20.70   $20.70  
  Purchase #5 $221.51   12.129%   $248.3769   $248.38   $248.40   $248.40  
  Purchase #6 $201.41   9.576%   $220.697   $220.70   $220.70   $220.70  
  Purchase #7 $141.71   13.597%   $160.9783   $160.98   $161.00   $161.00  
  7 purchase totals = $935.01       $1,023.5569   $1,023.57   $1,023.65   $1,023.60