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 $88.46   3.414%   $91.48   $91.48   $91.50   $91.50  
  Purchase #2 $222.92   13.605%   $253.2483   $253.25   $253.25   $253.20  
  Purchase #3 $217.79   4.150%   $226.8283   $226.83   $226.85   $226.80  
  Purchase #4 $236.99   13.322%   $268.5618   $268.56   $268.55   $268.60  
  Purchase #5 $26.64   12.708%   $30.0254   $30.03   $30.05   $30.00  
  Purchase #6 $165.87   12.572%   $186.7232   $186.72   $186.70   $186.70  
  Purchase #7 $207.61   3.248%   $214.3532   $214.35   $214.35   $214.40  
  7 purchase totals = $1,166.28       $1,271.2202   $1,271.22   $1,271.25   $1,271.20