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 $24.82   6.318%   $26.3881   $26.39   $26.40   $26.40  
  Purchase #2 $51.46   3.592%   $53.3084   $53.31   $53.30   $53.30  
  Purchase #3 $147.53   5.780%   $156.0572   $156.06   $156.05   $156.10  
  Purchase #4 $207.74   13.225%   $235.2136   $235.21   $235.20   $235.20  
  Purchase #5 $75.74   8.794%   $82.4006   $82.40   $82.40   $82.40  
  Purchase #6 $126.86   5.261%   $133.5341   $133.53   $133.55   $133.50  
  Purchase #7 $249.86   3.122%   $257.6606   $257.66   $257.65   $257.70  
  7 purchase totals = $884.01       $944.5626   $944.56   $944.55   $944.60