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 $120.94   4.629%   $126.5383   $126.54   $126.55   $126.50  
  Purchase #2 $160.95   3.159%   $166.0344   $166.03   $166.05   $166.00  
  Purchase #3 $174.77   4.284%   $182.2571   $182.26   $182.25   $182.30  
  Purchase #4 $239.54   3.782%   $248.5994   $248.60   $248.60   $248.60  
  Purchase #5 $130.91   3.540%   $135.5442   $135.54   $135.55   $135.50  
  Purchase #6 $155.45   3.317%   $160.6063   $160.61   $160.60   $160.60  
  Purchase #7 $206.28   13.216%   $233.542   $233.54   $233.55   $233.50  
  7 purchase totals = $1,188.84       $1,253.1217   $1,253.12   $1,253.15   $1,253.00