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 $244.93   8.618%   $266.0381   $266.04   $266.05   $266.00  
  Purchase #2 $117.84   8.804%   $128.2146   $128.21   $128.20   $128.20  
  Purchase #3 $104.87   5.334%   $110.4638   $110.46   $110.45   $110.50  
  Purchase #4 $192.72   13.457%   $218.6543   $218.65   $218.65   $218.70  
  Purchase #5 $104.95   9.587%   $115.0116   $115.01   $115.00   $115.00  
  Purchase #6 $51.45   8.827%   $55.9915   $55.99   $56.00   $56.00  
  Purchase #7 $164.55   13.803%   $187.2628   $187.26   $187.25   $187.30  
  7 purchase totals = $981.31       $1,081.6367   $1,081.62   $1,081.60   $1,081.70