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 $124.71   8.517%   $135.3316   $135.33   $135.35   $135.30  
  Purchase #2 $131.39   8.577%   $142.6593   $142.66   $142.65   $142.70  
  Purchase #3 $138.90   12.321%   $156.0139   $156.01   $156.00   $156.00  
  Purchase #4 $164.32   6.483%   $174.9729   $174.97   $174.95   $175.00  
  Purchase #5 $236.37   11.787%   $264.2309   $264.23   $264.25   $264.20  
  Purchase #6 $237.30   12.294%   $266.4737   $266.47   $266.45   $266.50  
  Purchase #7 $164.82   6.729%   $175.9107   $175.91   $175.90   $175.90  
  7 purchase totals = $1,197.81       $1,315.5930   $1,315.58   $1,315.55   $1,315.60