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 $65.39   6.605%   $69.709   $69.71   $69.70   $69.70  
  Purchase #2 $68.47   3.316%   $70.7405   $70.74   $70.75   $70.70  
  Purchase #3 $92.87   6.316%   $98.7357   $98.74   $98.75   $98.70  
  Purchase #4 $150.52   4.246%   $156.9111   $156.91   $156.90   $156.90  
  Purchase #5 $125.49   6.296%   $133.3909   $133.39   $133.40   $133.40  
  Purchase #6 $242.55   7.116%   $259.8099   $259.81   $259.80   $259.80  
  Purchase #7 $134.69   5.788%   $142.4859   $142.49   $142.50   $142.50  
  7 purchase totals = $879.98       $931.7830   $931.79   $931.80   $931.70