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 $207.96   13.871%   $236.8061   $236.81   $236.80   $236.80  
  Purchase #2 $215.45   5.199%   $226.6512   $226.65   $226.65   $226.70  
  Purchase #3 $21.32   10.569%   $23.5733   $23.57   $23.55   $23.60  
  Purchase #4 $138.65   5.318%   $146.0234   $146.02   $146.00   $146.00  
  Purchase #5 $89.78   5.229%   $94.4746   $94.47   $94.45   $94.50  
  Purchase #6 $248.67   7.196%   $266.5643   $266.56   $266.55   $266.60  
  Purchase #7 $88.71   4.272%   $92.4997   $92.50   $92.50   $92.50  
  7 purchase totals = $1,010.54       $1,086.5926   $1,086.58   $1,086.50   $1,086.70