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 $116.50   9.720%   $127.8238   $127.82   $127.80   $127.80  
  Purchase #2 $185.57   4.145%   $193.2619   $193.26   $193.25   $193.30  
  Purchase #3 $207.62   3.218%   $214.3012   $214.30   $214.30   $214.30  
  Purchase #4 $194.89   5.459%   $205.529   $205.53   $205.55   $205.50  
  Purchase #5 $179.32   9.159%   $195.7439   $195.74   $195.75   $195.70  
  Purchase #6 $164.49   13.292%   $186.354   $186.35   $186.35   $186.40  
  Purchase #7 $146.42   5.828%   $154.9534   $154.95   $154.95   $155.00  
  7 purchase totals = $1,194.81       $1,277.9672   $1,277.95   $1,277.95   $1,278.00