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 $114.64   10.238%   $126.3768   $126.38   $126.40   $126.40  
  Purchase #2 $221.70   6.824%   $236.8288   $236.83   $236.85   $236.80  
  Purchase #3 $47.31   5.654%   $49.9849   $49.98   $50.00   $50.00  
  Purchase #4 $222.67   11.831%   $249.0141   $249.01   $249.00   $249.00  
  Purchase #5 $76.97   5.674%   $81.3373   $81.34   $81.35   $81.30  
  Purchase #6 $71.89   6.836%   $76.8044   $76.80   $76.80   $76.80  
  Purchase #7 $41.56   3.367%   $42.9593   $42.96   $42.95   $43.00  
  7 purchase totals = $796.74       $863.3056   $863.30   $863.35   $863.30