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 $146.32   5.656%   $154.5959   $154.60   $154.60   $154.60  
  Purchase #2 $24.58   6.648%   $26.2141   $26.21   $26.20   $26.20  
  Purchase #3 $115.89   10.821%   $128.4305   $128.43   $128.45   $128.40  
  Purchase #4 $229.88   4.776%   $240.8591   $240.86   $240.85   $240.90  
  Purchase #5 $122.58   3.198%   $126.5001   $126.50   $126.50   $126.50  
  Purchase #6 $71.28   10.821%   $78.9932   $78.99   $79.00   $79.00  
  Purchase #7 $235.54   10.637%   $260.5944   $260.59   $260.60   $260.60  
  7 purchase totals = $946.07       $1,016.1873   $1,016.18   $1,016.20   $1,016.20