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 $55.38   8.770%   $60.2368   $60.24   $60.25   $60.20  
  Purchase #2 $145.25   12.356%   $163.1971   $163.20   $163.20   $163.20  
  Purchase #3 $230.98   7.659%   $248.6708   $248.67   $248.65   $248.70  
  Purchase #4 $249.43   4.512%   $260.6843   $260.68   $260.70   $260.70  
  Purchase #5 $24.67   6.475%   $26.2674   $26.27   $26.25   $26.30  
  Purchase #6 $103.38   7.285%   $110.9112   $110.91   $110.90   $110.90  
  Purchase #7 $11.66   8.815%   $12.6878   $12.69   $12.70   $12.70  
  7 purchase totals = $820.75       $882.6554   $882.66   $882.65   $882.70