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 $97.94   11.831%   $109.5273   $109.53   $109.55   $109.50  
  Purchase #2 $87.73   4.342%   $91.5392   $91.54   $91.55   $91.50  
  Purchase #3 $74.51   7.688%   $80.2383   $80.24   $80.25   $80.20  
  Purchase #4 $91.92   10.357%   $101.4402   $101.44   $101.45   $101.40  
  Purchase #5 $173.39   5.202%   $182.4097   $182.41   $182.40   $182.40  
  Purchase #6 $240.56   11.177%   $267.4474   $267.45   $267.45   $267.40  
  Purchase #7 $43.95   10.719%   $48.661   $48.66   $48.65   $48.70  
  7 purchase totals = $810.00       $881.2631   $881.27   $881.30   $881.10