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 $67.62   8.346%   $73.2636   $73.26   $73.25   $73.30  
  Purchase #2 $157.77   5.674%   $166.7219   $166.72   $166.70   $166.70  
  Purchase #3 $21.89   13.201%   $24.7797   $24.78   $24.80   $24.80  
  Purchase #4 $250.94   8.761%   $272.9249   $272.92   $272.90   $272.90  
  Purchase #5 $59.77   4.461%   $62.4363   $62.44   $62.45   $62.40  
  Purchase #6 $107.88   5.297%   $113.5944   $113.59   $113.60   $113.60  
  Purchase #7 $22.97   11.258%   $25.556   $25.56   $25.55   $25.60  
  7 purchase totals = $688.84       $739.2768   $739.27   $739.25   $739.30