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 $180.93   13.457%   $205.2778   $205.28   $205.30   $205.30  
  Purchase #2 $209.69   10.541%   $231.7934   $231.79   $231.80   $231.80  
  Purchase #3 $126.61   8.509%   $137.3832   $137.38   $137.40   $137.40  
  Purchase #4 $29.67   13.249%   $33.601   $33.60   $33.60   $33.60  
  Purchase #5 $196.59   5.206%   $206.8245   $206.82   $206.80   $206.80  
  Purchase #6 $207.25   11.686%   $231.4692   $231.47   $231.45   $231.50  
  Purchase #7 $196.96   6.775%   $210.304   $210.30   $210.30   $210.30  
  7 purchase totals = $1,147.70       $1,256.6531   $1,256.64   $1,256.65   $1,256.70