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 $239.91   6.115%   $254.5805   $254.58   $254.60   $254.60  
  Purchase #2 $136.99   8.546%   $148.6972   $148.70   $148.70   $148.70  
  Purchase #3 $14.44   5.771%   $15.2733   $15.27   $15.25   $15.30  
  Purchase #4 $198.87   11.476%   $221.6923   $221.69   $221.70   $221.70  
  Purchase #5 $27.72   4.235%   $28.8939   $28.89   $28.90   $28.90  
  Purchase #6 $160.25   7.688%   $172.57   $172.57   $172.55   $172.60  
  Purchase #7 $162.87   4.306%   $169.8832   $169.88   $169.90   $169.90  
  7 purchase totals = $941.05       $1,011.5904   $1,011.58   $1,011.60   $1,011.70