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 $60.25   11.255%   $67.0311   $67.03   $67.05   $67.00  
  Purchase #2 $67.70   7.521%   $72.7917   $72.79   $72.80   $72.80  
  Purchase #3 $248.91   6.450%   $264.9647   $264.96   $264.95   $265.00  
  Purchase #4 $184.39   12.555%   $207.5402   $207.54   $207.55   $207.50  
  Purchase #5 $170.99   8.620%   $185.7293   $185.73   $185.75   $185.70  
  Purchase #6 $155.47   5.711%   $164.3489   $164.35   $164.35   $164.30  
  Purchase #7 $192.61   8.759%   $209.4807   $209.48   $209.50   $209.50  
  7 purchase totals = $1,080.32       $1,171.8866   $1,171.88   $1,171.95   $1,171.80