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 $64.51   13.400%   $73.1543   $73.15   $73.15   $73.20  
  Purchase #2 $116.85   7.615%   $125.7481   $125.75   $125.75   $125.70  
  Purchase #3 $53.89   13.376%   $61.0983   $61.10   $61.10   $61.10  
  Purchase #4 $20.50   11.821%   $22.9233   $22.92   $22.90   $22.90  
  Purchase #5 $17.93   10.474%   $19.808   $19.81   $19.80   $19.80  
  Purchase #6 $45.32   4.602%   $47.4056   $47.41   $47.40   $47.40  
  Purchase #7 $46.97   11.659%   $52.4462   $52.45   $52.45   $52.40  
  7 purchase totals = $365.97       $402.5838   $402.59   $402.55   $402.50