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 $136.95   11.182%   $152.2637   $152.26   $152.25   $152.30  
  Purchase #2 $139.86   12.511%   $157.3579   $157.36   $157.35   $157.40  
  Purchase #3 $211.47   11.723%   $236.2606   $236.26   $236.25   $236.30  
  Purchase #4 $6.42   3.361%   $6.6358   $6.64   $6.65   $6.60  
  Purchase #5 $167.60   12.457%   $188.4779   $188.48   $188.50   $188.50  
  Purchase #6 $244.33   8.712%   $265.616   $265.62   $265.60   $265.60  
  Purchase #7 $91.58   8.857%   $99.6912   $99.69   $99.70   $99.70  
  7 purchase totals = $998.21       $1,106.3031   $1,106.31   $1,106.30   $1,106.40