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 $67.66   5.623%   $71.4645   $71.46   $71.45   $71.50  
  Purchase #2 $114.31   7.222%   $122.5655   $122.57   $122.55   $122.60  
  Purchase #3 $32.48   10.252%   $35.8098   $35.81   $35.80   $35.80  
  Purchase #4 $55.66   9.696%   $61.0568   $61.06   $61.05   $61.10  
  Purchase #5 $201.74   7.703%   $217.28   $217.28   $217.30   $217.30  
  Purchase #6 $221.81   13.266%   $251.2353   $251.24   $251.25   $251.20  
  Purchase #7 $249.60   8.824%   $271.6247   $271.62   $271.60   $271.60  
  7 purchase totals = $943.26       $1,031.0366   $1,031.04   $1,031.00   $1,031.10