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 $23.31   12.625%   $26.2529   $26.25   $26.25   $26.30  
  Purchase #2 $108.82   13.312%   $123.3061   $123.31   $123.30   $123.30  
  Purchase #3 $204.25   12.129%   $229.0235   $229.02   $229.00   $229.00  
  Purchase #4 $53.70   4.838%   $56.298   $56.30   $56.30   $56.30  
  Purchase #5 $127.75   12.200%   $143.3355   $143.34   $143.35   $143.30  
  Purchase #6 $11.95   13.695%   $13.5866   $13.59   $13.60   $13.60  
  Purchase #7 $94.69   12.787%   $106.798   $106.80   $106.80   $106.80  
  7 purchase totals = $624.47       $698.6006   $698.61   $698.60   $698.60