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 $90.83   11.335%   $101.1256   $101.13   $101.15   $101.10  
  Purchase #2 $245.54   8.395%   $266.1531   $266.15   $266.15   $266.20  
  Purchase #3 $83.28   4.516%   $87.0409   $87.04   $87.05   $87.00  
  Purchase #4 $73.66   5.230%   $77.5124   $77.51   $77.50   $77.50  
  Purchase #5 $167.55   7.857%   $180.7144   $180.71   $180.70   $180.70  
  Purchase #6 $185.33   11.516%   $206.6726   $206.67   $206.65   $206.70  
  Purchase #7 $15.93   3.241%   $16.4463   $16.45   $16.45   $16.40  
  7 purchase totals = $862.12       $935.6653   $935.66   $935.65   $935.60