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 $23.89   12.554%   $26.8892   $26.89   $26.90   $26.90  
  Purchase #2 $165.35   11.482%   $184.3355   $184.34   $184.35   $184.30  
  Purchase #3 $179.68   5.508%   $189.5768   $189.58   $189.60   $189.60  
  Purchase #4 $20.81   7.709%   $22.4142   $22.41   $22.40   $22.40  
  Purchase #5 $66.81   9.667%   $73.2685   $73.27   $73.25   $73.30  
  Purchase #6 $170.76   6.817%   $182.4007   $182.40   $182.40   $182.40  
  Purchase #7 $44.34   8.786%   $48.2357   $48.24   $48.25   $48.20  
  7 purchase totals = $671.64       $727.1206   $727.13   $727.15   $727.10