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 $53.66   11.788%   $59.9854   $59.99   $60.00   $60.00  
  Purchase #2 $48.98   13.294%   $55.4914   $55.49   $55.50   $55.50  
  Purchase #3 $5.75   13.389%   $6.5199   $6.52   $6.50   $6.50  
  Purchase #4 $41.66   11.804%   $46.5775   $46.58   $46.60   $46.60  
  Purchase #5 $21.54   3.619%   $22.3195   $22.32   $22.30   $22.30  
  Purchase #6 $60.95   12.384%   $68.498   $68.50   $68.50   $68.50  
  Purchase #7 $163.81   6.452%   $174.379   $174.38   $174.40   $174.40  
  7 purchase totals = $396.35       $433.7707   $433.78   $433.80   $433.80