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 $158.82   11.834%   $177.6148   $177.61   $177.60   $177.60  
  Purchase #2 $248.87   5.499%   $262.5554   $262.56   $262.55   $262.60  
  Purchase #3 $164.72   5.869%   $174.3874   $174.39   $174.40   $174.40  
  Purchase #4 $121.58   9.791%   $133.4839   $133.48   $133.50   $133.50  
  Purchase #5 $174.55   9.528%   $191.1811   $191.18   $191.20   $191.20  
  Purchase #6 $49.43   7.569%   $53.1714   $53.17   $53.15   $53.20  
  Purchase #7 $92.91   12.779%   $104.783   $104.78   $104.80   $104.80  
  7 purchase totals = $1,010.88       $1,097.1770   $1,097.17   $1,097.20   $1,097.30