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 $188.81   6.621%   $201.3111   $201.31   $201.30   $201.30  
  Purchase #2 $248.64   3.564%   $257.5015   $257.50   $257.50   $257.50  
  Purchase #3 $153.38   8.867%   $166.9802   $166.98   $167.00   $167.00  
  Purchase #4 $41.61   4.739%   $43.5819   $43.58   $43.60   $43.60  
  Purchase #5 $118.98   4.753%   $124.6351   $124.64   $124.65   $124.60  
  Purchase #6 $175.43   12.239%   $196.9009   $196.90   $196.90   $196.90  
  Purchase #7 $209.30   8.287%   $226.6447   $226.64   $226.65   $226.60  
  7 purchase totals = $1,136.15       $1,217.5554   $1,217.55   $1,217.60   $1,217.50