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 $58.51   10.873%   $64.8718   $64.87   $64.85   $64.90  
  Purchase #2 $239.76   9.495%   $262.5252   $262.53   $262.55   $262.50  
  Purchase #3 $215.95   13.244%   $244.5504   $244.55   $244.55   $244.60  
  Purchase #4 $210.51   3.677%   $218.2505   $218.25   $218.25   $218.30  
  Purchase #5 $33.58   4.685%   $35.1532   $35.15   $35.15   $35.20  
  Purchase #6 $175.45   5.285%   $184.7225   $184.72   $184.70   $184.70  
  Purchase #7 $56.66   6.440%   $60.3089   $60.31   $60.30   $60.30  
  7 purchase totals = $990.42       $1,070.3825   $1,070.38   $1,070.35   $1,070.50