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 $236.71   13.646%   $269.0114   $269.01   $269.00   $269.00  
  Purchase #2 $25.53   3.249%   $26.3595   $26.36   $26.35   $26.40  
  Purchase #3 $95.71   9.501%   $104.8034   $104.80   $104.80   $104.80  
  Purchase #4 $190.74   5.248%   $200.75   $200.75   $200.75   $200.80  
  Purchase #5 $184.47   13.601%   $209.5598   $209.56   $209.55   $209.60  
  Purchase #6 $105.69   8.688%   $114.8723   $114.87   $114.85   $114.90  
  Purchase #7 $93.78   7.299%   $100.625   $100.63   $100.65   $100.60  
  7 purchase totals = $932.63       $1,025.9814   $1,025.98   $1,025.95   $1,026.10