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 $163.81   8.754%   $178.1499   $178.15   $178.15   $178.10  
  Purchase #2 $179.42   13.515%   $203.6686   $203.67   $203.65   $203.70  
  Purchase #3 $64.78   13.664%   $73.6315   $73.63   $73.65   $73.60  
  Purchase #4 $17.87   7.870%   $19.2764   $19.28   $19.30   $19.30  
  Purchase #5 $13.35   4.794%   $13.99   $13.99   $14.00   $14.00  
  Purchase #6 $56.40   11.295%   $62.7704   $62.77   $62.75   $62.80  
  Purchase #7 $156.77   11.149%   $174.2483   $174.25   $174.25   $174.20  
  7 purchase totals = $652.40       $725.7351   $725.74   $725.75   $725.70