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 $9.65   13.475%   $10.9503   $10.95   $10.95   $11.00  
  Purchase #2 $180.39   12.278%   $202.5383   $202.54   $202.55   $202.50  
  Purchase #3 $63.97   12.269%   $71.8185   $71.82   $71.80   $71.80  
  Purchase #4 $97.65   6.486%   $103.9836   $103.98   $104.00   $104.00  
  Purchase #5 $64.45   10.587%   $71.2733   $71.27   $71.25   $71.30  
  Purchase #6 $176.39   8.204%   $190.861   $190.86   $190.85   $190.90  
  Purchase #7 $204.76   7.438%   $219.99   $219.99   $220.00   $220.00  
  7 purchase totals = $797.26       $871.4150   $871.41   $871.40   $871.50