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 $22.33   10.757%   $24.732   $24.73   $24.75   $24.70  
  Purchase #2 $65.26   11.305%   $72.6376   $72.64   $72.65   $72.60  
  Purchase #3 $81.42   6.289%   $86.5405   $86.54   $86.55   $86.50  
  Purchase #4 $37.99   3.724%   $39.4047   $39.40   $39.40   $39.40  
  Purchase #5 $193.93   11.632%   $216.4879   $216.49   $216.50   $216.50  
  Purchase #6 $43.74   10.871%   $48.495   $48.50   $48.50   $48.50  
  Purchase #7 $175.36   6.554%   $186.8531   $186.85   $186.85   $186.90  
  7 purchase totals = $620.03       $675.1508   $675.15   $675.20   $675.10