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 $55.89   3.115%   $57.631   $57.63   $57.65   $57.60  
  Purchase #2 $248.55   5.618%   $262.5135   $262.51   $262.50   $262.50  
  Purchase #3 $27.96   4.693%   $29.2722   $29.27   $29.25   $29.30  
  Purchase #4 $35.59   5.523%   $37.5556   $37.56   $37.55   $37.60  
  Purchase #5 $230.62   3.644%   $239.0238   $239.02   $239.00   $239.00  
  Purchase #6 $32.97   10.215%   $36.3379   $36.34   $36.35   $36.30  
  Purchase #7 $217.91   8.848%   $237.1907   $237.19   $237.20   $237.20  
  7 purchase totals = $849.49       $899.5247   $899.52   $899.50   $899.50