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 $76.62   7.272%   $82.1918   $82.19   $82.20   $82.20  
  Purchase #2 $32.85   8.411%   $35.613   $35.61   $35.60   $35.60  
  Purchase #3 $192.34   11.493%   $214.4456   $214.45   $214.45   $214.40  
  Purchase #4 $114.96   3.154%   $118.5858   $118.59   $118.60   $118.60  
  Purchase #5 $156.89   9.694%   $172.0989   $172.10   $172.10   $172.10  
  Purchase #6 $209.87   4.339%   $218.9763   $218.98   $219.00   $219.00  
  Purchase #7 $16.28   12.181%   $18.2631   $18.26   $18.25   $18.30  
  7 purchase totals = $799.81       $860.1745   $860.18   $860.20   $860.20