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 $184.41   12.311%   $207.1127   $207.11   $207.10   $207.10  
  Purchase #2 $66.62   11.373%   $74.1967   $74.20   $74.20   $74.20  
  Purchase #3 $162.88   8.530%   $176.7737   $176.77   $176.75   $176.80  
  Purchase #4 $144.69   3.354%   $149.5429   $149.54   $149.55   $149.50  
  Purchase #5 $134.75   3.264%   $139.1482   $139.15   $139.15   $139.10  
  Purchase #6 $179.47   9.166%   $195.9202   $195.92   $195.90   $195.90  
  Purchase #7 $17.53   6.848%   $18.7305   $18.73   $18.75   $18.70  
  7 purchase totals = $890.35       $961.4249   $961.42   $961.40   $961.30