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 $24.48   8.586%   $26.5819   $26.58   $26.60   $26.60  
  Purchase #2 $157.58   4.497%   $164.6664   $164.67   $164.65   $164.70  
  Purchase #3 $130.58   11.778%   $145.9597   $145.96   $145.95   $146.00  
  Purchase #4 $49.91   3.787%   $51.8001   $51.80   $51.80   $51.80  
  Purchase #5 $34.82   5.376%   $36.6919   $36.69   $36.70   $36.70  
  Purchase #6 $207.36   8.195%   $224.3532   $224.35   $224.35   $224.40  
  Purchase #7 $196.68   13.397%   $223.0292   $223.03   $223.05   $223.00  
  7 purchase totals = $801.41       $873.0824   $873.08   $873.10   $873.20