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 $38.69   13.173%   $43.7866   $43.79   $43.80   $43.80  
  Purchase #2 $81.25   11.714%   $90.7676   $90.77   $90.75   $90.80  
  Purchase #3 $206.37   11.570%   $230.247   $230.25   $230.25   $230.20  
  Purchase #4 $190.62   9.463%   $208.6584   $208.66   $208.65   $208.70  
  Purchase #5 $206.64   4.794%   $216.5463   $216.55   $216.55   $216.50  
  Purchase #6 $239.71   12.364%   $269.3477   $269.35   $269.35   $269.30  
  Purchase #7 $8.68   5.629%   $9.1686   $9.17   $9.15   $9.20  
  7 purchase totals = $971.96       $1,068.5222   $1,068.54   $1,068.50   $1,068.50