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 $56.60   5.292%   $59.5953   $59.60   $59.60   $59.60  
  Purchase #2 $80.49   8.298%   $87.1691   $87.17   $87.15   $87.20  
  Purchase #3 $162.45   3.499%   $168.1341   $168.13   $168.15   $168.10  
  Purchase #4 $114.26   8.759%   $124.268   $124.27   $124.25   $124.30  
  Purchase #5 $234.48   13.694%   $266.5897   $266.59   $266.60   $266.60  
  Purchase #6 $125.71   3.638%   $130.2833   $130.28   $130.30   $130.30  
  Purchase #7 $51.57   10.791%   $57.1349   $57.13   $57.15   $57.10  
  7 purchase totals = $825.56       $893.1744   $893.17   $893.20   $893.20