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 $222.68   10.798%   $246.725   $246.73   $246.75   $246.70  
  Purchase #2 $20.89   12.323%   $23.4643   $23.46   $23.45   $23.50  
  Purchase #3 $224.51   3.286%   $231.8874   $231.89   $231.90   $231.90  
  Purchase #4 $56.81   5.537%   $59.9556   $59.96   $59.95   $60.00  
  Purchase #5 $244.61   6.160%   $259.678   $259.68   $259.70   $259.70  
  Purchase #6 $198.59   4.528%   $207.5822   $207.58   $207.60   $207.60  
  Purchase #7 $77.46   11.631%   $86.4694   $86.47   $86.45   $86.50  
  7 purchase totals = $1,045.55       $1,115.7619   $1,115.77   $1,115.80   $1,115.90