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 $69.29   9.462%   $75.8462   $75.85   $75.85   $75.80  
  Purchase #2 $185.43   4.309%   $193.4202   $193.42   $193.40   $193.40  
  Purchase #3 $62.78   11.152%   $69.7812   $69.78   $69.80   $69.80  
  Purchase #4 $164.38   9.432%   $179.8843   $179.88   $179.90   $179.90  
  Purchase #5 $26.45   5.523%   $27.9108   $27.91   $27.90   $27.90  
  Purchase #6 $45.26   8.840%   $49.261   $49.26   $49.25   $49.30  
  Purchase #7 $240.71   7.137%   $257.8895   $257.89   $257.90   $257.90  
  7 purchase totals = $794.30       $853.9932   $853.99   $854.00   $854.00