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 $83.92   10.402%   $92.6494   $92.65   $92.65   $92.60  
  Purchase #2 $222.66   6.407%   $236.9258   $236.93   $236.95   $236.90  
  Purchase #3 $170.34   5.291%   $179.3527   $179.35   $179.35   $179.40  
  Purchase #4 $120.69   11.843%   $134.9833   $134.98   $135.00   $135.00  
  Purchase #5 $71.81   9.311%   $78.4962   $78.50   $78.50   $78.50  
  Purchase #6 $122.82   8.229%   $132.9269   $132.93   $132.95   $132.90  
  Purchase #7 $249.63   11.364%   $277.998   $278.00   $278.00   $278.00  
  7 purchase totals = $1,041.87       $1,133.3323   $1,133.34   $1,133.40   $1,133.30