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 $23.78   11.639%   $26.5478   $26.55   $26.55   $26.50  
  Purchase #2 $96.57   8.293%   $104.5786   $104.58   $104.60   $104.60  
  Purchase #3 $198.78   7.788%   $214.261   $214.26   $214.25   $214.30  
  Purchase #4 $214.95   5.576%   $226.9356   $226.94   $226.95   $226.90  
  Purchase #5 $161.36   4.322%   $168.334   $168.33   $168.35   $168.30  
  Purchase #6 $184.64   11.831%   $206.4848   $206.48   $206.50   $206.50  
  Purchase #7 $198.88   12.621%   $223.9806   $223.98   $224.00   $224.00  
  7 purchase totals = $1,078.96       $1,171.1224   $1,171.12   $1,171.20   $1,171.10