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 $65.92   11.787%   $73.69   $73.69   $73.70   $73.70  
  Purchase #2 $186.90   13.324%   $211.8026   $211.80   $211.80   $211.80  
  Purchase #3 $44.44   13.710%   $50.5327   $50.53   $50.55   $50.50  
  Purchase #4 $75.95   4.814%   $79.6062   $79.61   $79.60   $79.60  
  Purchase #5 $190.33   10.857%   $210.9941   $210.99   $211.00   $211.00  
  Purchase #6 $104.34   13.285%   $118.2016   $118.20   $118.20   $118.20  
  Purchase #7 $232.59   12.309%   $261.2195   $261.22   $261.20   $261.20  
  7 purchase totals = $900.47       $1,006.0467   $1,006.04   $1,006.05   $1,006.00