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 $68.48   13.847%   $77.9624   $77.96   $77.95   $78.00  
  Purchase #2 $208.35   8.475%   $226.0077   $226.01   $226.00   $226.00  
  Purchase #3 $123.99   11.127%   $137.7864   $137.79   $137.80   $137.80  
  Purchase #4 $182.98   9.299%   $199.9953   $200.00   $200.00   $200.00  
  Purchase #5 $247.79   5.747%   $262.0305   $262.03   $262.05   $262.00  
  Purchase #6 $13.50   9.228%   $14.7458   $14.75   $14.75   $14.70  
  Purchase #7 $46.93   12.664%   $52.8732   $52.87   $52.85   $52.90  
  7 purchase totals = $892.02       $971.4013   $971.41   $971.40   $971.40