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 $155.54   3.699%   $161.2934   $161.29   $161.30   $161.30  
  Purchase #2 $221.44   12.423%   $248.9495   $248.95   $248.95   $248.90  
  Purchase #3 $76.25   11.614%   $85.1057   $85.11   $85.10   $85.10  
  Purchase #4 $125.27   9.805%   $137.5527   $137.55   $137.55   $137.60  
  Purchase #5 $60.53   8.299%   $65.5534   $65.55   $65.55   $65.60  
  Purchase #6 $189.59   10.837%   $210.1359   $210.14   $210.15   $210.10  
  Purchase #7 $125.81   11.417%   $140.1737   $140.17   $140.15   $140.20  
  7 purchase totals = $954.43       $1,048.7643   $1,048.76   $1,048.75   $1,048.80