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 $146.71   5.611%   $154.9419   $154.94   $154.95   $154.90  
  Purchase #2 $188.51   11.365%   $209.9342   $209.93   $209.95   $209.90  
  Purchase #3 $58.39   6.578%   $62.2309   $62.23   $62.25   $62.20  
  Purchase #4 $250.81   7.224%   $268.9285   $268.93   $268.95   $268.90  
  Purchase #5 $243.65   9.653%   $267.1695   $267.17   $267.15   $267.20  
  Purchase #6 $207.90   3.797%   $215.794   $215.79   $215.80   $215.80  
  Purchase #7 $39.48   11.799%   $44.1382   $44.14   $44.15   $44.10  
  7 purchase totals = $1,135.45       $1,223.1372   $1,223.13   $1,223.20   $1,223.00