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 $53.55   7.157%   $57.3826   $57.38   $57.40   $57.40  
  Purchase #2 $169.57   6.705%   $180.9397   $180.94   $180.95   $180.90  
  Purchase #3 $16.40   13.765%   $18.6575   $18.66   $18.65   $18.70  
  Purchase #4 $106.49   11.774%   $119.0281   $119.03   $119.05   $119.00  
  Purchase #5 $232.44   7.719%   $250.382   $250.38   $250.40   $250.40  
  Purchase #6 $206.72   8.576%   $224.4483   $224.45   $224.45   $224.40  
  Purchase #7 $82.83   9.674%   $90.843   $90.84   $90.85   $90.80  
  7 purchase totals = $868.00       $941.6812   $941.68   $941.75   $941.60