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 $62.63   5.770%   $66.2438   $66.24   $66.25   $66.20  
  Purchase #2 $193.59   6.276%   $205.7397   $205.74   $205.75   $205.70  
  Purchase #3 $234.67   13.353%   $266.0055   $266.01   $266.00   $266.00  
  Purchase #4 $34.47   3.788%   $35.7757   $35.78   $35.80   $35.80  
  Purchase #5 $218.58   9.450%   $239.2358   $239.24   $239.25   $239.20  
  Purchase #6 $46.47   13.404%   $52.6988   $52.70   $52.70   $52.70  
  Purchase #7 $31.56   5.408%   $33.2668   $33.27   $33.25   $33.30  
  7 purchase totals = $821.97       $898.9661   $898.98   $899.00   $898.90