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 $61.39   8.780%   $66.78   $66.78   $66.80   $66.80  
  Purchase #2 $173.52   11.607%   $193.6605   $193.66   $193.65   $193.70  
  Purchase #3 $15.75   3.708%   $16.334   $16.33   $16.35   $16.30  
  Purchase #4 $194.51   12.404%   $218.637   $218.64   $218.65   $218.60  
  Purchase #5 $201.71   6.440%   $214.7001   $214.70   $214.70   $214.70  
  Purchase #6 $175.78   6.131%   $186.5571   $186.56   $186.55   $186.60  
  Purchase #7 $80.34   8.757%   $87.3754   $87.38   $87.40   $87.40  
  7 purchase totals = $903.00       $984.0441   $984.05   $984.10   $984.10