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 $240.79   11.578%   $268.6687   $268.67   $268.65   $268.70  
  Purchase #2 $237.47   12.730%   $267.6999   $267.70   $267.70   $267.70  
  Purchase #3 $86.45   7.273%   $92.7375   $92.74   $92.75   $92.70  
  Purchase #4 $79.38   8.544%   $86.1622   $86.16   $86.15   $86.20  
  Purchase #5 $227.81   6.654%   $242.9685   $242.97   $242.95   $243.00  
  Purchase #6 $121.44   12.303%   $136.3808   $136.38   $136.40   $136.40  
  Purchase #7 $216.77   6.579%   $231.0313   $231.03   $231.05   $231.00  
  7 purchase totals = $1,210.11       $1,325.6489   $1,325.65   $1,325.65   $1,325.70