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 $84.56   13.750%   $96.187   $96.19   $96.20   $96.20  
  Purchase #2 $245.69   9.393%   $268.7677   $268.77   $268.75   $268.80  
  Purchase #3 $25.49   8.285%   $27.6018   $27.60   $27.60   $27.60  
  Purchase #4 $163.81   9.285%   $179.0198   $179.02   $179.00   $179.00  
  Purchase #5 $21.78   8.569%   $23.6463   $23.65   $23.65   $23.60  
  Purchase #6 $56.31   8.355%   $61.0147   $61.01   $61.00   $61.00  
  Purchase #7 $23.76   4.575%   $24.847   $24.85   $24.85   $24.80  
  7 purchase totals = $621.40       $681.0843   $681.09   $681.05   $681.00