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 $208.76   12.621%   $235.1076   $235.11   $235.10   $235.10  
  Purchase #2 $105.57   6.704%   $112.6474   $112.65   $112.65   $112.60  
  Purchase #3 $207.92   12.369%   $233.6376   $233.64   $233.65   $233.60  
  Purchase #4 $232.76   12.149%   $261.038   $261.04   $261.05   $261.00  
  Purchase #5 $115.66   8.619%   $125.6287   $125.63   $125.65   $125.60  
  Purchase #6 $51.29   6.309%   $54.5259   $54.53   $54.55   $54.50  
  Purchase #7 $86.46   13.539%   $98.1658   $98.17   $98.15   $98.20  
  7 purchase totals = $1,008.42       $1,120.7510   $1,120.77   $1,120.80   $1,120.60