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 $223.98   13.763%   $254.8064   $254.81   $254.80   $254.80  
  Purchase #2 $53.76   6.770%   $57.3996   $57.40   $57.40   $57.40  
  Purchase #3 $171.25   11.341%   $190.6715   $190.67   $190.65   $190.70  
  Purchase #4 $205.85   9.215%   $224.8191   $224.82   $224.80   $224.80  
  Purchase #5 $57.33   8.742%   $62.3418   $62.34   $62.35   $62.30  
  Purchase #6 $228.28   11.589%   $254.7354   $254.74   $254.75   $254.70  
  Purchase #7 $247.80   8.624%   $269.1703   $269.17   $269.15   $269.20  
  7 purchase totals = $1,188.25       $1,313.9441   $1,313.95   $1,313.90   $1,313.90