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 $61.54   8.787%   $66.9475   $66.95   $66.95   $66.90  
  Purchase #2 $147.67   9.187%   $161.2364   $161.24   $161.25   $161.20  
  Purchase #3 $246.63   6.336%   $262.2565   $262.26   $262.25   $262.30  
  Purchase #4 $76.56   13.304%   $86.7455   $86.75   $86.75   $86.70  
  Purchase #5 $208.88   9.572%   $228.874   $228.87   $228.85   $228.90  
  Purchase #6 $152.99   11.871%   $171.1514   $171.15   $171.15   $171.20  
  Purchase #7 $13.58   8.279%   $14.7043   $14.70   $14.70   $14.70  
  7 purchase totals = $907.85       $991.9156   $991.92   $991.90   $991.90