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 $165.54   12.182%   $185.7061   $185.71   $185.70   $185.70  
  Purchase #2 $95.34   8.400%   $103.3486   $103.35   $103.35   $103.30  
  Purchase #3 $63.82   10.556%   $70.5568   $70.56   $70.55   $70.60  
  Purchase #4 $150.58   7.361%   $161.6642   $161.66   $161.65   $161.70  
  Purchase #5 $129.62   7.595%   $139.4646   $139.46   $139.45   $139.50  
  Purchase #6 $241.91   8.687%   $262.9247   $262.92   $262.90   $262.90  
  Purchase #7 $54.71   13.203%   $61.9334   $61.93   $61.95   $61.90  
  7 purchase totals = $901.52       $985.5984   $985.59   $985.55   $985.60