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 $208.84   11.853%   $233.5938   $233.59   $233.60   $233.60  
  Purchase #2 $156.33   12.474%   $175.8306   $175.83   $175.85   $175.80  
  Purchase #3 $180.69   11.682%   $201.7982   $201.80   $201.80   $201.80  
  Purchase #4 $65.72   6.187%   $69.7861   $69.79   $69.80   $69.80  
  Purchase #5 $160.92   8.259%   $174.2104   $174.21   $174.20   $174.20  
  Purchase #6 $182.87   3.436%   $189.1534   $189.15   $189.15   $189.20  
  Purchase #7 $161.40   6.686%   $172.1912   $172.19   $172.20   $172.20  
  7 purchase totals = $1,116.77       $1,216.5637   $1,216.56   $1,216.60   $1,216.60