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 $68.45   10.499%   $75.6366   $75.64   $75.65   $75.60  
  Purchase #2 $146.91   9.410%   $160.7342   $160.73   $160.75   $160.70  
  Purchase #3 $93.54   13.177%   $105.8658   $105.87   $105.85   $105.90  
  Purchase #4 $201.76   10.440%   $222.8237   $222.82   $222.80   $222.80  
  Purchase #5 $246.37   6.506%   $262.3988   $262.40   $262.40   $262.40  
  Purchase #6 $123.73   10.579%   $136.8194   $136.82   $136.80   $136.80  
  Purchase #7 $24.40   10.383%   $26.9335   $26.93   $26.95   $26.90  
  7 purchase totals = $905.16       $991.2120   $991.21   $991.20   $991.10