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 $225.59   9.635%   $247.3256   $247.33   $247.35   $247.30  
  Purchase #2 $208.70   13.396%   $236.6575   $236.66   $236.65   $236.70  
  Purchase #3 $149.28   4.821%   $156.4768   $156.48   $156.50   $156.50  
  Purchase #4 $121.54   5.285%   $127.9634   $127.96   $127.95   $128.00  
  Purchase #5 $69.46   9.591%   $76.1219   $76.12   $76.10   $76.10  
  Purchase #6 $20.54   7.271%   $22.0335   $22.03   $22.05   $22.00  
  Purchase #7 $24.28   8.134%   $26.2549   $26.25   $26.25   $26.30  
  7 purchase totals = $819.39       $892.8336   $892.83   $892.85   $892.90