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 $66.34   6.819%   $70.8637   $70.86   $70.85   $70.90  
  Purchase #2 $152.86   4.799%   $160.1958   $160.20   $160.20   $160.20  
  Purchase #3 $208.63   9.665%   $228.7941   $228.79   $228.80   $228.80  
  Purchase #4 $234.81   11.316%   $261.3811   $261.38   $261.40   $261.40  
  Purchase #5 $46.35   4.751%   $48.5521   $48.55   $48.55   $48.60  
  Purchase #6 $175.93   7.338%   $188.8397   $188.84   $188.85   $188.80  
  Purchase #7 $226.65   5.605%   $239.3537   $239.35   $239.35   $239.40  
  7 purchase totals = $1,111.57       $1,197.9802   $1,197.97   $1,198.00   $1,198.10