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 $56.89   11.215%   $63.2702   $63.27   $63.25   $63.30  
  Purchase #2 $120.75   7.416%   $129.7048   $129.70   $129.70   $129.70  
  Purchase #3 $67.90   12.322%   $76.2666   $76.27   $76.25   $76.30  
  Purchase #4 $231.57   6.695%   $247.0736   $247.07   $247.05   $247.10  
  Purchase #5 $140.92   6.695%   $150.3546   $150.35   $150.35   $150.40  
  Purchase #6 $87.66   3.803%   $90.9937   $90.99   $91.00   $91.00  
  Purchase #7 $242.81   9.706%   $266.3771   $266.38   $266.40   $266.40  
  7 purchase totals = $948.50       $1,024.0406   $1,024.03   $1,024.00   $1,024.20