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 $70.46   6.535%   $75.0646   $75.06   $75.05   $75.10  
  Purchase #2 $94.44   10.602%   $104.4525   $104.45   $104.45   $104.50  
  Purchase #3 $78.53   3.393%   $81.1945   $81.19   $81.20   $81.20  
  Purchase #4 $239.76   7.676%   $258.164   $258.16   $258.15   $258.20  
  Purchase #5 $247.89   7.432%   $266.3132   $266.31   $266.30   $266.30  
  Purchase #6 $124.52   7.406%   $133.742   $133.74   $133.75   $133.70  
  Purchase #7 $49.41   11.771%   $55.2261   $55.23   $55.25   $55.20  
  7 purchase totals = $905.01       $974.1569   $974.14   $974.15   $974.20