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 $55.81   13.582%   $63.3901   $63.39   $63.40   $63.40  
  Purchase #2 $230.70   6.778%   $246.3368   $246.34   $246.35   $246.30  
  Purchase #3 $124.25   3.464%   $128.554   $128.55   $128.55   $128.60  
  Purchase #4 $86.77   9.608%   $95.1069   $95.11   $95.10   $95.10  
  Purchase #5 $169.47   13.242%   $191.9112   $191.91   $191.90   $191.90  
  Purchase #6 $231.71   8.723%   $251.9221   $251.92   $251.90   $251.90  
  Purchase #7 $176.81   9.846%   $194.2187   $194.22   $194.20   $194.20  
  7 purchase totals = $1,075.52       $1,171.4398   $1,171.44   $1,171.40   $1,171.40