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 $184.31   11.407%   $205.3342   $205.33   $205.35   $205.30  
  Purchase #2 $245.38   13.653%   $278.8817   $278.88   $278.90   $278.90  
  Purchase #3 $135.92   3.789%   $141.07   $141.07   $141.05   $141.10  
  Purchase #4 $53.34   6.788%   $56.9607   $56.96   $56.95   $57.00  
  Purchase #5 $224.61   9.194%   $245.2606   $245.26   $245.25   $245.30  
  Purchase #6 $180.57   4.381%   $188.4808   $188.48   $188.50   $188.50  
  Purchase #7 $227.46   8.859%   $247.6107   $247.61   $247.60   $247.60  
  7 purchase totals = $1,251.59       $1,363.5987   $1,363.59   $1,363.60   $1,363.70