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 $222.89   8.859%   $242.6358   $242.64   $242.65   $242.60  
  Purchase #2 $218.95   12.651%   $246.6494   $246.65   $246.65   $246.60  
  Purchase #3 $72.94   8.371%   $79.0458   $79.05   $79.05   $79.00  
  Purchase #4 $55.41   13.346%   $62.805   $62.81   $62.80   $62.80  
  Purchase #5 $236.61   3.484%   $244.8535   $244.85   $244.85   $244.90  
  Purchase #6 $143.80   11.758%   $160.708   $160.71   $160.70   $160.70  
  Purchase #7 $45.94   5.760%   $48.5861   $48.59   $48.60   $48.60  
  7 purchase totals = $996.54       $1,085.2836   $1,085.30   $1,085.30   $1,085.20