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 $85.89   11.346%   $95.6351   $95.64   $95.65   $95.60  
  Purchase #2 $250.59   3.207%   $258.6264   $258.63   $258.65   $258.60  
  Purchase #3 $116.32   4.400%   $121.4381   $121.44   $121.45   $121.40  
  Purchase #4 $193.59   8.265%   $209.5902   $209.59   $209.60   $209.60  
  Purchase #5 $30.47   12.218%   $34.1928   $34.19   $34.20   $34.20  
  Purchase #6 $240.89   7.345%   $258.5834   $258.58   $258.60   $258.60  
  Purchase #7 $243.67   8.560%   $264.5282   $264.53   $264.55   $264.50  
  7 purchase totals = $1,161.42       $1,242.5942   $1,242.60   $1,242.70   $1,242.50