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 $222.61   8.577%   $241.7033   $241.70   $241.70   $241.70  
  Purchase #2 $209.87   10.118%   $231.1046   $231.10   $231.10   $231.10  
  Purchase #3 $163.37   12.726%   $184.1605   $184.16   $184.15   $184.20  
  Purchase #4 $110.86   7.541%   $119.22   $119.22   $119.20   $119.20  
  Purchase #5 $120.83   8.741%   $131.3918   $131.39   $131.40   $131.40  
  Purchase #6 $167.88   6.678%   $179.091   $179.09   $179.10   $179.10  
  Purchase #7 $162.65   13.527%   $184.6517   $184.65   $184.65   $184.70  
  7 purchase totals = $1,158.07       $1,271.3229   $1,271.31   $1,271.30   $1,271.40