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 $23.98   13.174%   $27.1391   $27.14   $27.15   $27.10  
  Purchase #2 $72.54   12.839%   $81.8534   $81.85   $81.85   $81.90  
  Purchase #3 $127.71   12.356%   $143.4898   $143.49   $143.50   $143.50  
  Purchase #4 $232.86   12.371%   $261.6671   $261.67   $261.65   $261.70  
  Purchase #5 $72.71   4.391%   $75.9027   $75.90   $75.90   $75.90  
  Purchase #6 $204.25   3.580%   $211.5622   $211.56   $211.55   $211.60  
  Purchase #7 $135.57   8.652%   $147.2995   $147.30   $147.30   $147.30  
  7 purchase totals = $869.62       $948.9138   $948.91   $948.90   $949.00