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 $209.80   6.604%   $223.6552   $223.66   $223.65   $223.70  
  Purchase #2 $35.72   7.241%   $38.3065   $38.31   $38.30   $38.30  
  Purchase #3 $42.72   4.605%   $44.6873   $44.69   $44.70   $44.70  
  Purchase #4 $40.81   8.295%   $44.1952   $44.20   $44.20   $44.20  
  Purchase #5 $117.82   4.261%   $122.8403   $122.84   $122.85   $122.80  
  Purchase #6 $200.55   6.359%   $213.303   $213.30   $213.30   $213.30  
  Purchase #7 $152.83   7.255%   $163.9178   $163.92   $163.90   $163.90  
  7 purchase totals = $800.25       $850.9053   $850.92   $850.90   $850.90