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 $117.58   3.806%   $122.0551   $122.06   $122.05   $122.10  
  Purchase #2 $237.89   6.287%   $252.8461   $252.85   $252.85   $252.80  
  Purchase #3 $35.38   8.396%   $38.3505   $38.35   $38.35   $38.40  
  Purchase #4 $172.55   5.438%   $181.9333   $181.93   $181.95   $181.90  
  Purchase #5 $136.90   12.190%   $153.5881   $153.59   $153.60   $153.60  
  Purchase #6 $229.77   9.198%   $250.9042   $250.90   $250.90   $250.90  
  Purchase #7 $92.85   4.176%   $96.7274   $96.73   $96.75   $96.70  
  7 purchase totals = $1,022.92       $1,096.4047   $1,096.41   $1,096.45   $1,096.40