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 $57.61   13.157%   $65.1897   $65.19   $65.20   $65.20  
  Purchase #2 $195.47   11.648%   $218.2383   $218.24   $218.25   $218.20  
  Purchase #3 $191.28   7.110%   $204.88   $204.88   $204.90   $204.90  
  Purchase #4 $201.49   13.466%   $228.6226   $228.62   $228.60   $228.60  
  Purchase #5 $227.49   7.338%   $244.1832   $244.18   $244.20   $244.20  
  Purchase #6 $250.45   3.657%   $259.609   $259.61   $259.60   $259.60  
  Purchase #7 $236.76   8.469%   $256.8112   $256.81   $256.80   $256.80  
  7 purchase totals = $1,360.55       $1,477.5340   $1,477.53   $1,477.55   $1,477.50