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 $75.33   11.779%   $84.2031   $84.20   $84.20   $84.20  
  Purchase #2 $177.93   3.204%   $183.6309   $183.63   $183.65   $183.60  
  Purchase #3 $90.86   8.333%   $98.4314   $98.43   $98.45   $98.40  
  Purchase #4 $196.71   6.109%   $208.727   $208.73   $208.75   $208.70  
  Purchase #5 $55.49   6.321%   $58.9975   $59.00   $59.00   $59.00  
  Purchase #6 $90.55   8.412%   $98.1671   $98.17   $98.15   $98.20  
  Purchase #7 $166.50   5.469%   $175.6059   $175.61   $175.60   $175.60  
  7 purchase totals = $853.37       $907.7629   $907.77   $907.80   $907.70