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 $213.58   12.613%   $240.5188   $240.52   $240.50   $240.50  
  Purchase #2 $149.50   11.447%   $166.6133   $166.61   $166.60   $166.60  
  Purchase #3 $179.54   3.856%   $186.4631   $186.46   $186.45   $186.50  
  Purchase #4 $71.36   10.606%   $78.9284   $78.93   $78.95   $78.90  
  Purchase #5 $171.51   13.690%   $194.9897   $194.99   $195.00   $195.00  
  Purchase #6 $237.68   9.570%   $260.426   $260.43   $260.45   $260.40  
  Purchase #7 $249.43   5.147%   $262.2682   $262.27   $262.25   $262.30  
  7 purchase totals = $1,272.60       $1,390.2075   $1,390.21   $1,390.20   $1,390.20