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 $222.70   13.722%   $253.2589   $253.26   $253.25   $253.30  
  Purchase #2 $163.71   12.293%   $183.8349   $183.83   $183.85   $183.80  
  Purchase #3 $114.88   10.379%   $126.8034   $126.80   $126.80   $126.80  
  Purchase #4 $179.95   3.566%   $186.367   $186.37   $186.35   $186.40  
  Purchase #5 $109.41   4.743%   $114.5993   $114.60   $114.60   $114.60  
  Purchase #6 $169.36   3.394%   $175.1081   $175.11   $175.10   $175.10  
  Purchase #7 $110.49   3.489%   $114.345   $114.35   $114.35   $114.30  
  7 purchase totals = $1,070.50       $1,154.3166   $1,154.32   $1,154.30   $1,154.30