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 $10.61   4.190%   $11.0546   $11.05   $11.05   $11.10  
  Purchase #2 $123.46   13.192%   $139.7468   $139.75   $139.75   $139.70  
  Purchase #3 $168.81   9.489%   $184.8284   $184.83   $184.85   $184.80  
  Purchase #4 $157.70   8.719%   $171.4499   $171.45   $171.45   $171.40  
  Purchase #5 $154.52   11.806%   $172.7626   $172.76   $172.75   $172.80  
  Purchase #6 $214.89   8.866%   $233.9421   $233.94   $233.95   $233.90  
  Purchase #7 $121.31   13.774%   $138.0192   $138.02   $138.00   $138.00  
  7 purchase totals = $951.30       $1,051.8036   $1,051.80   $1,051.80   $1,051.70