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 $232.28   11.493%   $258.9759   $258.98   $259.00   $259.00  
  Purchase #2 $213.83   8.738%   $232.5145   $232.51   $232.50   $232.50  
  Purchase #3 $14.99   6.437%   $15.9549   $15.95   $15.95   $16.00  
  Purchase #4 $240.61   7.853%   $259.5051   $259.51   $259.50   $259.50  
  Purchase #5 $198.99   12.500%   $223.8638   $223.86   $223.85   $223.90  
  Purchase #6 $30.56   3.451%   $31.6146   $31.61   $31.60   $31.60  
  Purchase #7 $170.75   5.140%   $179.5266   $179.53   $179.55   $179.50  
  7 purchase totals = $1,102.01       $1,201.9554   $1,201.95   $1,201.95   $1,202.00