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 $233.82   13.872%   $266.2555   $266.26   $266.25   $266.30  
  Purchase #2 $249.55   12.294%   $280.2297   $280.23   $280.25   $280.20  
  Purchase #3 $195.40   8.177%   $211.3779   $211.38   $211.40   $211.40  
  Purchase #4 $176.73   12.178%   $198.2522   $198.25   $198.25   $198.30  
  Purchase #5 $49.76   11.580%   $55.5222   $55.52   $55.50   $55.50  
  Purchase #6 $32.97   8.837%   $35.8836   $35.88   $35.90   $35.90  
  Purchase #7 $159.40   11.164%   $177.1954   $177.20   $177.20   $177.20  
  7 purchase totals = $1,097.63       $1,224.7165   $1,224.72   $1,224.75   $1,224.80