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 $68.59   12.806%   $77.3736   $77.37   $77.35   $77.40  
  Purchase #2 $214.82   11.105%   $238.6758   $238.68   $238.70   $238.70  
  Purchase #3 $53.37   5.684%   $56.4036   $56.40   $56.40   $56.40  
  Purchase #4 $181.36   8.214%   $196.2569   $196.26   $196.25   $196.30  
  Purchase #5 $19.77   12.786%   $22.2978   $22.30   $22.30   $22.30  
  Purchase #6 $190.43   12.592%   $214.4089   $214.41   $214.40   $214.40  
  Purchase #7 $121.57   12.125%   $136.3104   $136.31   $136.30   $136.30  
  7 purchase totals = $849.91       $941.7270   $941.73   $941.70   $941.80