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 $22.91   11.204%   $25.4768   $25.48   $25.50   $25.50  
  Purchase #2 $217.43   13.130%   $245.9786   $245.98   $246.00   $246.00  
  Purchase #3 $158.58   11.441%   $176.7231   $176.72   $176.70   $176.70  
  Purchase #4 $17.30   6.429%   $18.4122   $18.41   $18.40   $18.40  
  Purchase #5 $161.78   3.725%   $167.8063   $167.81   $167.80   $167.80  
  Purchase #6 $93.87   7.455%   $100.868   $100.87   $100.85   $100.90  
  Purchase #7 $37.40   11.571%   $41.7276   $41.73   $41.75   $41.70  
  7 purchase totals = $709.27       $776.9926   $777.00   $777.00   $777.00