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 $63.73   7.623%   $68.5881   $68.59   $68.60   $68.60  
  Purchase #2 $229.32   6.539%   $244.3152   $244.32   $244.30   $244.30  
  Purchase #3 $107.74   5.436%   $113.5967   $113.60   $113.60   $113.60  
  Purchase #4 $226.82   13.531%   $257.511   $257.51   $257.50   $257.50  
  Purchase #5 $117.48   6.446%   $125.0528   $125.05   $125.05   $125.10  
  Purchase #6 $224.38   10.111%   $247.0671   $247.07   $247.05   $247.10  
  Purchase #7 $66.57   7.285%   $71.4196   $71.42   $71.40   $71.40  
  7 purchase totals = $1,036.04       $1,127.5505   $1,127.56   $1,127.50   $1,127.60