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 $241.85   11.357%   $269.3169   $269.32   $269.30   $269.30  
  Purchase #2 $34.67   7.276%   $37.1926   $37.19   $37.20   $37.20  
  Purchase #3 $207.58   9.870%   $228.0681   $228.07   $228.05   $228.10  
  Purchase #4 $63.41   5.243%   $66.7346   $66.73   $66.75   $66.70  
  Purchase #5 $230.95   11.873%   $258.3707   $258.37   $258.35   $258.40  
  Purchase #6 $41.95   10.654%   $46.4194   $46.42   $46.40   $46.40  
  Purchase #7 $63.30   3.627%   $65.5959   $65.60   $65.60   $65.60  
  7 purchase totals = $883.71       $971.6982   $971.70   $971.65   $971.70