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 $240.76   13.662%   $273.6526   $273.65   $273.65   $273.70  
  Purchase #2 $247.97   6.408%   $263.8599   $263.86   $263.85   $263.90  
  Purchase #3 $67.62   7.517%   $72.703   $72.70   $72.70   $72.70  
  Purchase #4 $97.32   13.250%   $110.2149   $110.21   $110.20   $110.20  
  Purchase #5 $98.38   12.159%   $110.342   $110.34   $110.35   $110.30  
  Purchase #6 $127.88   13.310%   $144.9008   $144.90   $144.90   $144.90  
  Purchase #7 $239.65   8.391%   $259.759   $259.76   $259.75   $259.80  
  7 purchase totals = $1,119.58       $1,235.4322   $1,235.42   $1,235.40   $1,235.50