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 $124.36   13.504%   $141.1536   $141.15   $141.15   $141.20  
  Purchase #2 $75.97   10.255%   $83.7607   $83.76   $83.75   $83.80  
  Purchase #3 $15.75   8.723%   $17.1239   $17.12   $17.10   $17.10  
  Purchase #4 $248.48   13.787%   $282.7379   $282.74   $282.75   $282.70  
  Purchase #5 $211.93   10.766%   $234.7464   $234.75   $234.75   $234.70  
  Purchase #6 $157.80   5.642%   $166.7031   $166.70   $166.70   $166.70  
  Purchase #7 $160.70   11.410%   $179.0359   $179.04   $179.05   $179.00  
  7 purchase totals = $994.99       $1,105.2615   $1,105.26   $1,105.25   $1,105.20