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 $57.39   10.236%   $63.2644   $63.26   $63.25   $63.30  
  Purchase #2 $66.92   3.595%   $69.3258   $69.33   $69.35   $69.30  
  Purchase #3 $23.97   9.123%   $26.1568   $26.16   $26.15   $26.20  
  Purchase #4 $196.85   5.287%   $207.2575   $207.26   $207.25   $207.30  
  Purchase #5 $164.93   6.245%   $175.2299   $175.23   $175.25   $175.20  
  Purchase #6 $244.26   12.499%   $274.7901   $274.79   $274.80   $274.80  
  Purchase #7 $33.50   3.171%   $34.5623   $34.56   $34.55   $34.60  
  7 purchase totals = $787.82       $850.5868   $850.59   $850.60   $850.70