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 $211.94   3.258%   $218.845   $218.85   $218.85   $218.80  
  Purchase #2 $66.99   3.479%   $69.3206   $69.32   $69.30   $69.30  
  Purchase #3 $46.97   8.724%   $51.0677   $51.07   $51.05   $51.10  
  Purchase #4 $198.99   7.431%   $213.7769   $213.78   $213.80   $213.80  
  Purchase #5 $170.27   13.874%   $193.8933   $193.89   $193.90   $193.90  
  Purchase #6 $53.47   12.430%   $60.1163   $60.12   $60.10   $60.10  
  Purchase #7 $141.82   9.871%   $155.8191   $155.82   $155.80   $155.80  
  7 purchase totals = $890.45       $962.8389   $962.85   $962.80   $962.80