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 $123.67   6.418%   $131.6071   $131.61   $131.60   $131.60  
  Purchase #2 $228.68   13.381%   $259.2797   $259.28   $259.30   $259.30  
  Purchase #3 $14.96   13.146%   $16.9266   $16.93   $16.95   $16.90  
  Purchase #4 $228.58   3.524%   $236.6352   $236.64   $236.65   $236.60  
  Purchase #5 $32.85   11.382%   $36.589   $36.59   $36.60   $36.60  
  Purchase #6 $52.97   6.519%   $56.4231   $56.42   $56.40   $56.40  
  Purchase #7 $174.50   11.818%   $195.1224   $195.12   $195.10   $195.10  
  7 purchase totals = $856.21       $932.5831   $932.59   $932.60   $932.50