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 $86.58   11.214%   $96.2891   $96.29   $96.30   $96.30  
  Purchase #2 $165.66   8.683%   $180.0443   $180.04   $180.05   $180.00  
  Purchase #3 $207.53   3.108%   $213.98   $213.98   $214.00   $214.00  
  Purchase #4 $163.84   5.256%   $172.4514   $172.45   $172.45   $172.50  
  Purchase #5 $12.87   13.555%   $14.6145   $14.61   $14.60   $14.60  
  Purchase #6 $104.74   8.564%   $113.7099   $113.71   $113.70   $113.70  
  Purchase #7 $226.52   9.615%   $248.2999   $248.30   $248.30   $248.30  
  7 purchase totals = $967.74       $1,039.3891   $1,039.38   $1,039.40   $1,039.40