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 $220.71   11.601%   $246.3146   $246.31   $246.30   $246.30  
  Purchase #2 $12.61   5.583%   $13.314   $13.31   $13.30   $13.30  
  Purchase #3 $250.54   12.747%   $282.4763   $282.48   $282.50   $282.50  
  Purchase #4 $141.82   11.351%   $157.918   $157.92   $157.90   $157.90  
  Purchase #5 $162.28   10.671%   $179.5969   $179.60   $179.60   $179.60  
  Purchase #6 $228.75   12.329%   $256.9526   $256.95   $256.95   $257.00  
  Purchase #7 $71.86   8.482%   $77.9552   $77.96   $77.95   $78.00  
  7 purchase totals = $1,088.57       $1,214.5276   $1,214.53   $1,214.50   $1,214.60