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 $52.40   8.279%   $56.7382   $56.74   $56.75   $56.70  
  Purchase #2 $248.92   8.267%   $269.4982   $269.50   $269.50   $269.50  
  Purchase #3 $233.88   10.471%   $258.3696   $258.37   $258.35   $258.40  
  Purchase #4 $141.66   13.126%   $160.2543   $160.25   $160.25   $160.30  
  Purchase #5 $75.51   5.611%   $79.7469   $79.75   $79.75   $79.70  
  Purchase #6 $157.95   3.566%   $163.5825   $163.58   $163.60   $163.60  
  Purchase #7 $84.75   5.764%   $89.635   $89.64   $89.65   $89.60  
  7 purchase totals = $995.07       $1,077.8247   $1,077.83   $1,077.85   $1,077.80