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 $68.37   10.614%   $75.6268   $75.63   $75.65   $75.60  
  Purchase #2 $201.41   5.428%   $212.3425   $212.34   $212.35   $212.30  
  Purchase #3 $99.87   13.247%   $113.0998   $113.10   $113.10   $113.10  
  Purchase #4 $61.78   5.354%   $65.0877   $65.09   $65.10   $65.10  
  Purchase #5 $215.30   6.213%   $228.6766   $228.68   $228.70   $228.70  
  Purchase #6 $11.79   10.426%   $13.0192   $13.02   $13.00   $13.00  
  Purchase #7 $178.30   8.531%   $193.5108   $193.51   $193.50   $193.50  
  7 purchase totals = $836.82       $901.3634   $901.37   $901.40   $901.30