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 $69.37   5.744%   $73.3546   $73.35   $73.35   $73.40  
  Purchase #2 $119.32   8.811%   $129.8333   $129.83   $129.85   $129.80  
  Purchase #3 $178.48   11.281%   $198.6143   $198.61   $198.60   $198.60  
  Purchase #4 $77.80   10.851%   $86.2421   $86.24   $86.25   $86.20  
  Purchase #5 $167.28   4.502%   $174.8109   $174.81   $174.80   $174.80  
  Purchase #6 $57.66   10.626%   $63.787   $63.79   $63.80   $63.80  
  Purchase #7 $240.71   6.652%   $256.722   $256.72   $256.70   $256.70  
  7 purchase totals = $910.62       $983.3642   $983.35   $983.35   $983.30