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 $244.59   9.685%   $268.2785   $268.28   $268.30   $268.30  
  Purchase #2 $113.93   4.666%   $119.246   $119.25   $119.25   $119.20  
  Purchase #3 $164.73   5.735%   $174.1773   $174.18   $174.20   $174.20  
  Purchase #4 $192.55   6.773%   $205.5914   $205.59   $205.60   $205.60  
  Purchase #5 $178.53   11.264%   $198.6396   $198.64   $198.65   $198.60  
  Purchase #6 $226.72   8.620%   $246.2633   $246.26   $246.25   $246.30  
  Purchase #7 $107.50   12.419%   $120.8504   $120.85   $120.85   $120.90  
  7 purchase totals = $1,228.55       $1,333.0465   $1,333.05   $1,333.10   $1,333.10