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 $218.94   9.436%   $239.5992   $239.60   $239.60   $239.60  
  Purchase #2 $113.80   10.484%   $125.7308   $125.73   $125.75   $125.70  
  Purchase #3 $79.95   9.623%   $87.6436   $87.64   $87.65   $87.60  
  Purchase #4 $207.93   6.149%   $220.7156   $220.72   $220.70   $220.70  
  Purchase #5 $53.52   6.874%   $57.199   $57.20   $57.20   $57.20  
  Purchase #6 $41.87   7.832%   $45.1493   $45.15   $45.15   $45.10  
  Purchase #7 $222.64   12.487%   $250.4411   $250.44   $250.45   $250.40  
  7 purchase totals = $938.65       $1,026.4786   $1,026.48   $1,026.50   $1,026.30