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 $249.32   5.144%   $262.145   $262.15   $262.15   $262.10  
  Purchase #2 $205.52   9.736%   $225.5294   $225.53   $225.55   $225.50  
  Purchase #3 $78.36   6.401%   $83.3758   $83.38   $83.40   $83.40  
  Purchase #4 $95.83   12.397%   $107.71   $107.71   $107.70   $107.70  
  Purchase #5 $153.25   5.768%   $162.0895   $162.09   $162.10   $162.10  
  Purchase #6 $214.71   4.640%   $224.6725   $224.67   $224.65   $224.70  
  Purchase #7 $172.68   8.585%   $187.5046   $187.50   $187.50   $187.50  
  7 purchase totals = $1,169.67       $1,253.0268   $1,253.03   $1,253.05   $1,253.00