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 $57.67   9.280%   $63.0218   $63.02   $63.00   $63.00  
  Purchase #2 $47.64   13.781%   $54.2053   $54.21   $54.20   $54.20  
  Purchase #3 $23.63   12.186%   $26.5096   $26.51   $26.50   $26.50  
  Purchase #4 $114.81   7.149%   $123.0178   $123.02   $123.00   $123.00  
  Purchase #5 $245.38   5.344%   $258.4931   $258.49   $258.50   $258.50  
  Purchase #6 $232.51   4.797%   $243.6635   $243.66   $243.65   $243.70  
  Purchase #7 $53.99   11.456%   $60.1751   $60.18   $60.20   $60.20  
  7 purchase totals = $775.63       $829.0862   $829.09   $829.05   $829.10