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 $118.61   4.378%   $123.8027   $123.80   $123.80   $123.80  
  Purchase #2 $247.77   5.518%   $261.4419   $261.44   $261.45   $261.40  
  Purchase #3 $50.83   11.190%   $56.5179   $56.52   $56.50   $56.50  
  Purchase #4 $58.49   4.260%   $60.9817   $60.98   $61.00   $61.00  
  Purchase #5 $214.71   13.271%   $243.2042   $243.20   $243.20   $243.20  
  Purchase #6 $250.49   13.128%   $283.3743   $283.37   $283.35   $283.40  
  Purchase #7 $126.85   10.216%   $139.809   $139.81   $139.80   $139.80  
  7 purchase totals = $1,067.75       $1,169.1317   $1,169.12   $1,169.10   $1,169.10