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 $23.93   12.501%   $26.9215   $26.92   $26.90   $26.90  
  Purchase #2 $183.77   11.775%   $205.4089   $205.41   $205.40   $205.40  
  Purchase #3 $86.87   6.198%   $92.2542   $92.25   $92.25   $92.30  
  Purchase #4 $58.37   5.705%   $61.7   $61.70   $61.70   $61.70  
  Purchase #5 $36.78   9.207%   $40.1663   $40.17   $40.15   $40.20  
  Purchase #6 $172.48   4.260%   $179.8276   $179.83   $179.85   $179.80  
  Purchase #7 $107.39   12.215%   $120.5077   $120.51   $120.50   $120.50  
  7 purchase totals = $669.59       $726.7862   $726.79   $726.75   $726.80