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 $207.39   9.387%   $226.8577   $226.86   $226.85   $226.90  
  Purchase #2 $106.87   7.512%   $114.8981   $114.90   $114.90   $114.90  
  Purchase #3 $113.80   10.225%   $125.4361   $125.44   $125.45   $125.40  
  Purchase #4 $26.53   11.694%   $29.6324   $29.63   $29.65   $29.60  
  Purchase #5 $63.80   10.335%   $70.3937   $70.39   $70.40   $70.40  
  Purchase #6 $11.35   11.472%   $12.6521   $12.65   $12.65   $12.70  
  Purchase #7 $195.97   3.274%   $202.3861   $202.39   $202.40   $202.40  
  7 purchase totals = $725.71       $782.2562   $782.26   $782.30   $782.30