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 $63.95   8.686%   $69.5047   $69.50   $69.50   $69.50  
  Purchase #2 $237.35   13.292%   $268.8986   $268.90   $268.90   $268.90  
  Purchase #3 $173.83   9.748%   $190.7749   $190.77   $190.75   $190.80  
  Purchase #4 $245.25   9.571%   $268.7229   $268.72   $268.70   $268.70  
  Purchase #5 $200.55   9.680%   $219.9632   $219.96   $219.95   $220.00  
  Purchase #6 $191.25   5.806%   $202.354   $202.35   $202.35   $202.40  
  Purchase #7 $123.90   8.564%   $134.5108   $134.51   $134.50   $134.50  
  7 purchase totals = $1,236.08       $1,354.7291   $1,354.71   $1,354.65   $1,354.80