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 $56.34   9.614%   $61.7565   $61.76   $61.75   $61.80  
  Purchase #2 $228.33   7.704%   $245.9205   $245.92   $245.90   $245.90  
  Purchase #3 $56.51   3.195%   $58.3155   $58.32   $58.30   $58.30  
  Purchase #4 $163.27   3.719%   $169.342   $169.34   $169.35   $169.30  
  Purchase #5 $182.89   7.296%   $196.2337   $196.23   $196.25   $196.20  
  Purchase #6 $143.93   9.775%   $157.9992   $158.00   $158.00   $158.00  
  Purchase #7 $156.45   13.116%   $176.97   $176.97   $176.95   $177.00  
  7 purchase totals = $987.72       $1,066.5374   $1,066.54   $1,066.50   $1,066.50