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 $118.95   12.642%   $133.9877   $133.99   $134.00   $134.00  
  Purchase #2 $15.41   7.626%   $16.5852   $16.59   $16.60   $16.60  
  Purchase #3 $52.51   10.867%   $58.2163   $58.22   $58.20   $58.20  
  Purchase #4 $211.29   11.442%   $235.4658   $235.47   $235.45   $235.50  
  Purchase #5 $201.99   12.151%   $226.5338   $226.53   $226.55   $226.50  
  Purchase #6 $71.64   13.346%   $81.2011   $81.20   $81.20   $81.20  
  Purchase #7 $102.85   10.745%   $113.9012   $113.90   $113.90   $113.90  
  7 purchase totals = $774.64       $865.8911   $865.90   $865.90   $865.90