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 $23.91   6.757%   $25.5256   $25.53   $25.55   $25.50  
  Purchase #2 $16.53   7.328%   $17.7413   $17.74   $17.75   $17.70  
  Purchase #3 $40.56   11.319%   $45.151   $45.15   $45.15   $45.20  
  Purchase #4 $250.64   4.545%   $262.0316   $262.03   $262.05   $262.00  
  Purchase #5 $147.55   3.775%   $153.12   $153.12   $153.10   $153.10  
  Purchase #6 $236.88   6.871%   $253.156   $253.16   $253.15   $253.20  
  Purchase #7 $246.61   8.298%   $267.0737   $267.07   $267.05   $267.10  
  7 purchase totals = $962.68       $1,023.7992   $1,023.80   $1,023.80   $1,023.80