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 $232.49   12.655%   $261.9116   $261.91   $261.90   $261.90  
  Purchase #2 $175.43   6.457%   $186.7575   $186.76   $186.75   $186.80  
  Purchase #3 $184.94   4.646%   $193.5323   $193.53   $193.55   $193.50  
  Purchase #4 $167.75   5.158%   $176.4025   $176.40   $176.40   $176.40  
  Purchase #5 $181.52   8.785%   $197.4665   $197.47   $197.45   $197.50  
  Purchase #6 $70.25   5.464%   $74.0885   $74.09   $74.10   $74.10  
  Purchase #7 $150.77   11.795%   $168.5533   $168.55   $168.55   $168.60  
  7 purchase totals = $1,163.15       $1,258.7122   $1,258.71   $1,258.70   $1,258.80