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 $232.57   5.360%   $245.0358   $245.04   $245.05   $245.00  
  Purchase #2 $104.82   11.853%   $117.2443   $117.24   $117.25   $117.20  
  Purchase #3 $79.88   12.321%   $89.722   $89.72   $89.70   $89.70  
  Purchase #4 $200.51   3.724%   $207.977   $207.98   $208.00   $208.00  
  Purchase #5 $111.78   3.653%   $115.8633   $115.86   $115.85   $115.90  
  Purchase #6 $161.53   3.542%   $167.2514   $167.25   $167.25   $167.30  
  Purchase #7 $14.50   9.771%   $15.9168   $15.92   $15.90   $15.90  
  7 purchase totals = $905.59       $959.0106   $959.01   $959.00   $959.00