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 $191.49   8.752%   $208.2492   $208.25   $208.25   $208.20  
  Purchase #2 $218.80   13.745%   $248.8741   $248.87   $248.85   $248.90  
  Purchase #3 $164.83   11.196%   $183.2844   $183.28   $183.30   $183.30  
  Purchase #4 $66.31   10.421%   $73.2202   $73.22   $73.20   $73.20  
  Purchase #5 $178.87   4.709%   $187.293   $187.29   $187.30   $187.30  
  Purchase #6 $177.70   9.537%   $194.6472   $194.65   $194.65   $194.60  
  Purchase #7 $21.56   6.589%   $22.9806   $22.98   $23.00   $23.00  
  7 purchase totals = $1,019.56       $1,118.5487   $1,118.54   $1,118.55   $1,118.50