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 $154.61   9.665%   $169.5531   $169.55   $169.55   $169.60  
  Purchase #2 $39.96   4.285%   $41.6723   $41.67   $41.65   $41.70  
  Purchase #3 $241.65   8.701%   $262.676   $262.68   $262.70   $262.70  
  Purchase #4 $54.55   5.798%   $57.7128   $57.71   $57.70   $57.70  
  Purchase #5 $71.70   6.627%   $76.4516   $76.45   $76.45   $76.50  
  Purchase #6 $53.89   7.309%   $57.8288   $57.83   $57.85   $57.80  
  Purchase #7 $87.62   6.572%   $93.3784   $93.38   $93.40   $93.40  
  7 purchase totals = $703.98       $759.2730   $759.27   $759.30   $759.40