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 $104.94   13.299%   $118.896   $118.90   $118.90   $118.90  
  Purchase #2 $40.97   9.129%   $44.7102   $44.71   $44.70   $44.70  
  Purchase #3 $243.33   8.234%   $263.3658   $263.37   $263.35   $263.40  
  Purchase #4 $225.29   10.108%   $248.0623   $248.06   $248.05   $248.10  
  Purchase #5 $239.62   9.710%   $262.8871   $262.89   $262.90   $262.90  
  Purchase #6 $174.30   8.220%   $188.6275   $188.63   $188.65   $188.60  
  Purchase #7 $218.37   12.710%   $246.1248   $246.12   $246.10   $246.10  
  7 purchase totals = $1,246.82       $1,372.6737   $1,372.68   $1,372.65   $1,372.70