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 $208.27   13.789%   $236.9884   $236.99   $237.00   $237.00  
  Purchase #2 $15.95   7.861%   $17.2038   $17.20   $17.20   $17.20  
  Purchase #3 $249.43   7.838%   $268.9803   $268.98   $269.00   $269.00  
  Purchase #4 $28.34   12.357%   $31.842   $31.84   $31.85   $31.80  
  Purchase #5 $229.94   12.288%   $258.195   $258.20   $258.20   $258.20  
  Purchase #6 $200.47   13.404%   $227.341   $227.34   $227.35   $227.30  
  Purchase #7 $91.92   11.558%   $102.5441   $102.54   $102.55   $102.50  
  7 purchase totals = $1,024.32       $1,143.0946   $1,143.09   $1,143.15   $1,143.00