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 $207.66   13.464%   $235.6193   $235.62   $235.60   $235.60  
  Purchase #2 $90.99   8.631%   $98.8433   $98.84   $98.85   $98.80  
  Purchase #3 $164.87   8.344%   $178.6268   $178.63   $178.65   $178.60  
  Purchase #4 $186.63   10.749%   $206.6909   $206.69   $206.70   $206.70  
  Purchase #5 $49.91   10.180%   $54.9908   $54.99   $55.00   $55.00  
  Purchase #6 $142.29   9.689%   $156.0765   $156.08   $156.10   $156.10  
  Purchase #7 $62.65   11.241%   $69.6925   $69.69   $69.70   $69.70  
  7 purchase totals = $905.00       $1,000.5401   $1,000.54   $1,000.60   $1,000.50