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 $218.49   13.856%   $248.764   $248.76   $248.75   $248.80  
  Purchase #2 $112.96   11.255%   $125.6736   $125.67   $125.65   $125.70  
  Purchase #3 $240.34   11.856%   $268.8347   $268.83   $268.85   $268.80  
  Purchase #4 $71.97   11.841%   $80.492   $80.49   $80.50   $80.50  
  Purchase #5 $190.87   6.234%   $202.7688   $202.77   $202.75   $202.80  
  Purchase #6 $213.60   13.359%   $242.1348   $242.13   $242.15   $242.10  
  Purchase #7 $98.71   10.225%   $108.8031   $108.80   $108.80   $108.80  
  7 purchase totals = $1,146.94       $1,277.4710   $1,277.45   $1,277.45   $1,277.50