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 $202.83   6.452%   $215.9166   $215.92   $215.90   $215.90  
  Purchase #2 $232.68   11.656%   $259.8012   $259.80   $259.80   $259.80  
  Purchase #3 $47.42   11.330%   $52.7927   $52.79   $52.80   $52.80  
  Purchase #4 $191.36   8.625%   $207.8648   $207.86   $207.85   $207.90  
  Purchase #5 $238.85   12.791%   $269.4013   $269.40   $269.40   $269.40  
  Purchase #6 $243.54   10.531%   $269.1872   $269.19   $269.20   $269.20  
  Purchase #7 $27.56   11.775%   $30.8052   $30.81   $30.80   $30.80  
  7 purchase totals = $1,184.24       $1,305.7690   $1,305.77   $1,305.75   $1,305.80