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 $214.97   11.465%   $239.6163   $239.62   $239.60   $239.60  
  Purchase #2 $53.57   7.526%   $57.6017   $57.60   $57.60   $57.60  
  Purchase #3 $191.81   4.455%   $200.3551   $200.36   $200.35   $200.40  
  Purchase #4 $174.96   10.536%   $193.3938   $193.39   $193.40   $193.40  
  Purchase #5 $143.54   8.762%   $156.117   $156.12   $156.10   $156.10  
  Purchase #6 $41.33   12.874%   $46.6508   $46.65   $46.65   $46.70  
  Purchase #7 $83.68   4.574%   $87.5075   $87.51   $87.50   $87.50  
  7 purchase totals = $903.86       $981.2422   $981.25   $981.20   $981.30