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 $103.95   13.672%   $118.162   $118.16   $118.15   $118.20  
  Purchase #2 $71.27   10.396%   $78.6792   $78.68   $78.70   $78.70  
  Purchase #3 $68.34   12.326%   $76.7636   $76.76   $76.75   $76.80  
  Purchase #4 $242.34   3.694%   $251.292   $251.29   $251.30   $251.30  
  Purchase #5 $145.74   12.689%   $164.2329   $164.23   $164.25   $164.20  
  Purchase #6 $179.55   12.712%   $202.3744   $202.37   $202.35   $202.40  
  Purchase #7 $53.79   8.589%   $58.41   $58.41   $58.40   $58.40  
  7 purchase totals = $864.98       $949.9141   $949.90   $949.90   $950.00