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 $226.86   11.350%   $252.6086   $252.61   $252.60   $252.60  
  Purchase #2 $104.47   13.287%   $118.3509   $118.35   $118.35   $118.40  
  Purchase #3 $161.73   9.748%   $177.4954   $177.50   $177.50   $177.50  
  Purchase #4 $112.25   4.854%   $117.6986   $117.70   $117.70   $117.70  
  Purchase #5 $192.71   8.571%   $209.2272   $209.23   $209.25   $209.20  
  Purchase #6 $172.40   6.469%   $183.5526   $183.55   $183.55   $183.60  
  Purchase #7 $244.40   9.183%   $266.8433   $266.84   $266.85   $266.80  
  7 purchase totals = $1,214.82       $1,325.7766   $1,325.78   $1,325.80   $1,325.80