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 $66.57   10.322%   $73.4414   $73.44   $73.45   $73.40  
  Purchase #2 $214.41   4.699%   $224.4851   $224.49   $224.50   $224.50  
  Purchase #3 $163.95   9.675%   $179.8122   $179.81   $179.80   $179.80  
  Purchase #4 $25.86   8.385%   $28.0284   $28.03   $28.05   $28.00  
  Purchase #5 $75.62   8.347%   $81.932   $81.93   $81.95   $81.90  
  Purchase #6 $113.95   11.209%   $126.7227   $126.72   $126.70   $126.70  
  Purchase #7 $167.41   6.732%   $178.68   $178.68   $178.70   $178.70  
  7 purchase totals = $827.77       $893.1018   $893.10   $893.15   $893.00