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 $241.39   9.589%   $264.5369   $264.54   $264.55   $264.50  
  Purchase #2 $249.42   12.525%   $280.6599   $280.66   $280.65   $280.70  
  Purchase #3 $67.25   4.786%   $70.4686   $70.47   $70.45   $70.50  
  Purchase #4 $152.42   4.349%   $159.0487   $159.05   $159.05   $159.00  
  Purchase #5 $217.38   6.384%   $231.2575   $231.26   $231.25   $231.30  
  Purchase #6 $145.68   5.705%   $153.991   $153.99   $154.00   $154.00  
  Purchase #7 $78.65   12.665%   $88.611   $88.61   $88.60   $88.60  
  7 purchase totals = $1,152.19       $1,248.5736   $1,248.58   $1,248.55   $1,248.60