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 $210.47   12.441%   $236.6546   $236.65   $236.65   $236.70  
  Purchase #2 $186.85   6.302%   $198.6253   $198.63   $198.65   $198.60  
  Purchase #3 $174.37   10.836%   $193.2647   $193.26   $193.25   $193.30  
  Purchase #4 $86.85   13.732%   $98.7762   $98.78   $98.80   $98.80  
  Purchase #5 $71.70   3.187%   $73.9851   $73.99   $74.00   $74.00  
  Purchase #6 $139.91   12.789%   $157.8031   $157.80   $157.80   $157.80  
  Purchase #7 $72.58   6.375%   $77.207   $77.21   $77.20   $77.20  
  7 purchase totals = $942.73       $1,036.3160   $1,036.32   $1,036.35   $1,036.40