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 $56.73   4.862%   $59.4882   $59.49   $59.50   $59.50  
  Purchase #2 $239.91   5.687%   $253.5537   $253.55   $253.55   $253.60  
  Purchase #3 $67.90   4.178%   $70.7369   $70.74   $70.75   $70.70  
  Purchase #4 $155.64   13.324%   $176.3775   $176.38   $176.40   $176.40  
  Purchase #5 $134.94   6.279%   $143.4129   $143.41   $143.40   $143.40  
  Purchase #6 $234.40   8.235%   $253.7028   $253.70   $253.70   $253.70  
  Purchase #7 $113.76   3.617%   $117.8747   $117.87   $117.85   $117.90  
  7 purchase totals = $1,003.28       $1,075.1467   $1,075.14   $1,075.15   $1,075.20