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 $241.78   9.182%   $263.9802   $263.98   $264.00   $264.00  
  Purchase #2 $69.33   3.262%   $71.5915   $71.59   $71.60   $71.60  
  Purchase #3 $154.72   8.366%   $167.6639   $167.66   $167.65   $167.70  
  Purchase #4 $149.29   3.614%   $154.6853   $154.69   $154.70   $154.70  
  Purchase #5 $169.55   8.274%   $183.5786   $183.58   $183.60   $183.60  
  Purchase #6 $219.81   13.275%   $248.9898   $248.99   $249.00   $249.00  
  Purchase #7 $203.88   10.349%   $224.9795   $224.98   $225.00   $225.00  
  7 purchase totals = $1,208.36       $1,315.4688   $1,315.47   $1,315.55   $1,315.60