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 $56.54   9.649%   $61.9955   $62.00   $62.00   $62.00  
  Purchase #2 $197.99   5.419%   $208.7191   $208.72   $208.70   $208.70  
  Purchase #3 $234.70   10.229%   $258.7075   $258.71   $258.70   $258.70  
  Purchase #4 $205.41   13.428%   $232.9925   $232.99   $233.00   $233.00  
  Purchase #5 $165.49   3.394%   $171.1067   $171.11   $171.10   $171.10  
  Purchase #6 $130.27   5.108%   $136.9242   $136.92   $136.90   $136.90  
  Purchase #7 $25.96   10.534%   $28.6946   $28.69   $28.70   $28.70  
  7 purchase totals = $1,016.36       $1,099.1401   $1,099.14   $1,099.10   $1,099.10