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 $248.99   8.270%   $269.5815   $269.58   $269.60   $269.60  
  Purchase #2 $141.66   10.471%   $156.4932   $156.49   $156.50   $156.50  
  Purchase #3 $131.66   11.780%   $147.1695   $147.17   $147.15   $147.20  
  Purchase #4 $238.77   11.389%   $265.9635   $265.96   $265.95   $266.00  
  Purchase #5 $206.90   9.566%   $226.6921   $226.69   $226.70   $226.70  
  Purchase #6 $174.74   4.690%   $182.9353   $182.94   $182.95   $182.90  
  Purchase #7 $173.60   12.266%   $194.8938   $194.89   $194.90   $194.90  
  7 purchase totals = $1,316.32       $1,443.7289   $1,443.72   $1,443.75   $1,443.80