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 $34.98   13.845%   $39.823   $39.82   $39.80   $39.80  
  Purchase #2 $200.87   5.359%   $211.6346   $211.63   $211.65   $211.60  
  Purchase #3 $62.77   5.501%   $66.223   $66.22   $66.20   $66.20  
  Purchase #4 $241.41   10.354%   $266.4056   $266.41   $266.40   $266.40  
  Purchase #5 $52.83   3.447%   $54.6511   $54.65   $54.65   $54.70  
  Purchase #6 $224.41   5.687%   $237.1722   $237.17   $237.15   $237.20  
  Purchase #7 $54.46   8.440%   $59.0564   $59.06   $59.05   $59.10  
  7 purchase totals = $871.73       $934.9659   $934.96   $934.90   $935.00