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 $34.49   11.277%   $38.3794   $38.38   $38.40   $38.40  
  Purchase #2 $77.68   10.269%   $85.657   $85.66   $85.65   $85.70  
  Purchase #3 $211.99   3.159%   $218.6868   $218.69   $218.70   $218.70  
  Purchase #4 $205.54   4.324%   $214.4275   $214.43   $214.45   $214.40  
  Purchase #5 $162.57   9.577%   $178.1393   $178.14   $178.15   $178.10  
  Purchase #6 $40.92   3.453%   $42.333   $42.33   $42.35   $42.30  
  Purchase #7 $55.65   3.588%   $57.6467   $57.65   $57.65   $57.60  
  7 purchase totals = $788.84       $835.2697   $835.28   $835.35   $835.20