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 $241.70   8.612%   $262.5152   $262.52   $262.50   $262.50  
  Purchase #2 $148.33   11.853%   $165.9116   $165.91   $165.90   $165.90  
  Purchase #3 $115.78   12.719%   $130.5061   $130.51   $130.50   $130.50  
  Purchase #4 $222.89   11.664%   $248.8879   $248.89   $248.90   $248.90  
  Purchase #5 $155.40   12.664%   $175.0799   $175.08   $175.10   $175.10  
  Purchase #6 $130.77   11.127%   $145.3208   $145.32   $145.30   $145.30  
  Purchase #7 $24.57   7.394%   $26.3867   $26.39   $26.40   $26.40  
  7 purchase totals = $1,039.44       $1,154.6082   $1,154.62   $1,154.60   $1,154.60