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 $164.83   8.850%   $179.4175   $179.42   $179.40   $179.40  
  Purchase #2 $135.47   4.693%   $141.8276   $141.83   $141.85   $141.80  
  Purchase #3 $123.64   7.122%   $132.4456   $132.45   $132.45   $132.40  
  Purchase #4 $25.71   8.209%   $27.8205   $27.82   $27.80   $27.80  
  Purchase #5 $216.88   8.756%   $235.87   $235.87   $235.85   $235.90  
  Purchase #6 $81.33   6.569%   $86.6726   $86.67   $86.65   $86.70  
  Purchase #7 $207.35   10.843%   $229.833   $229.83   $229.85   $229.80  
  7 purchase totals = $955.21       $1,033.8868   $1,033.89   $1,033.85   $1,033.80