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 $180.88   8.548%   $196.3416   $196.34   $196.35   $196.30  
  Purchase #2 $237.43   3.865%   $246.6067   $246.61   $246.60   $246.60  
  Purchase #3 $200.42   8.337%   $217.129   $217.13   $217.15   $217.10  
  Purchase #4 $238.50   4.691%   $249.688   $249.69   $249.70   $249.70  
  Purchase #5 $215.97   5.146%   $227.0838   $227.08   $227.10   $227.10  
  Purchase #6 $21.71   13.522%   $24.6456   $24.65   $24.65   $24.60  
  Purchase #7 $155.85   11.166%   $173.2522   $173.25   $173.25   $173.30  
  7 purchase totals = $1,250.76       $1,334.7469   $1,334.75   $1,334.80   $1,334.70