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 $164.61   11.144%   $182.9541   $182.95   $182.95   $183.00  
  Purchase #2 $155.41   5.751%   $164.3476   $164.35   $164.35   $164.30  
  Purchase #3 $241.72   11.609%   $269.7813   $269.78   $269.80   $269.80  
  Purchase #4 $21.87   10.862%   $24.2455   $24.25   $24.25   $24.20  
  Purchase #5 $136.37   9.629%   $149.5011   $149.50   $149.50   $149.50  
  Purchase #6 $201.50   13.839%   $229.3856   $229.39   $229.40   $229.40  
  Purchase #7 $17.37   12.756%   $19.5857   $19.59   $19.60   $19.60  
  7 purchase totals = $938.85       $1,039.8009   $1,039.81   $1,039.85   $1,039.80