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 $60.96   13.466%   $69.1689   $69.17   $69.15   $69.20  
  Purchase #2 $100.85   5.329%   $106.2243   $106.22   $106.20   $106.20  
  Purchase #3 $227.77   9.641%   $249.7293   $249.73   $249.75   $249.70  
  Purchase #4 $122.41   4.689%   $128.1498   $128.15   $128.15   $128.10  
  Purchase #5 $74.35   10.185%   $81.9225   $81.92   $81.90   $81.90  
  Purchase #6 $28.62   7.424%   $30.7447   $30.74   $30.75   $30.70  
  Purchase #7 $119.96   4.775%   $125.6881   $125.69   $125.70   $125.70  
  7 purchase totals = $734.92       $791.6276   $791.62   $791.60   $791.50