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 $77.33   6.176%   $82.1059   $82.11   $82.10   $82.10  
  Purchase #2 $93.28   8.661%   $101.359   $101.36   $101.35   $101.40  
  Purchase #3 $15.63   6.558%   $16.655   $16.66   $16.65   $16.70  
  Purchase #4 $8.37   12.471%   $9.4138   $9.41   $9.40   $9.40  
  Purchase #5 $115.83   7.218%   $124.1906   $124.19   $124.20   $124.20  
  Purchase #6 $184.87   8.195%   $200.0201   $200.02   $200.00   $200.00  
  Purchase #7 $162.99   7.816%   $175.7293   $175.73   $175.75   $175.70  
  7 purchase totals = $658.30       $709.4737   $709.48   $709.45   $709.50