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 $239.26   11.226%   $266.1193   $266.12   $266.10   $266.10  
  Purchase #2 $175.83   4.751%   $184.1837   $184.18   $184.20   $184.20  
  Purchase #3 $237.47   8.293%   $257.1634   $257.16   $257.15   $257.20  
  Purchase #4 $113.86   11.723%   $127.2078   $127.21   $127.20   $127.20  
  Purchase #5 $186.74   12.851%   $210.738   $210.74   $210.75   $210.70  
  Purchase #6 $104.60   12.761%   $117.948   $117.95   $117.95   $117.90  
  Purchase #7 $35.47   4.825%   $37.1814   $37.18   $37.20   $37.20  
  7 purchase totals = $1,093.23       $1,200.5416   $1,200.54   $1,200.55   $1,200.50