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 $75.87   4.478%   $79.2675   $79.27   $79.25   $79.30  
  Purchase #2 $162.82   7.819%   $175.5509   $175.55   $175.55   $175.60  
  Purchase #3 $201.59   13.564%   $228.9337   $228.93   $228.95   $228.90  
  Purchase #4 $130.76   10.818%   $144.9056   $144.91   $144.90   $144.90  
  Purchase #5 $145.58   8.566%   $158.0504   $158.05   $158.05   $158.10  
  Purchase #6 $225.49   13.810%   $256.6302   $256.63   $256.65   $256.60  
  Purchase #7 $198.96   11.691%   $222.2204   $222.22   $222.20   $222.20  
  7 purchase totals = $1,141.07       $1,265.5587   $1,265.56   $1,265.55   $1,265.60