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 $246.75   11.122%   $274.1935   $274.19   $274.20   $274.20  
  Purchase #2 $38.80   12.299%   $43.572   $43.57   $43.55   $43.60  
  Purchase #3 $51.33   5.177%   $53.9874   $53.99   $54.00   $54.00  
  Purchase #4 $161.83   10.839%   $179.3708   $179.37   $179.35   $179.40  
  Purchase #5 $186.63   10.779%   $206.7468   $206.75   $206.75   $206.70  
  Purchase #6 $162.57   7.873%   $175.3691   $175.37   $175.35   $175.40  
  Purchase #7 $140.45   8.641%   $152.5863   $152.59   $152.60   $152.60  
  7 purchase totals = $988.36       $1,085.8259   $1,085.83   $1,085.80   $1,085.90