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 $33.79   8.737%   $36.7422   $36.74   $36.75   $36.70  
  Purchase #2 $72.87   5.524%   $76.8953   $76.90   $76.90   $76.90  
  Purchase #3 $196.60   5.868%   $208.1365   $208.14   $208.15   $208.10  
  Purchase #4 $23.71   4.294%   $24.7281   $24.73   $24.75   $24.70  
  Purchase #5 $70.36   13.249%   $79.682   $79.68   $79.70   $79.70  
  Purchase #6 $178.72   11.259%   $198.8421   $198.84   $198.85   $198.80  
  Purchase #7 $131.34   11.801%   $146.8394   $146.84   $146.85   $146.80  
  7 purchase totals = $707.39       $771.8656   $771.87   $771.95   $771.70