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 $152.54   9.867%   $167.5911   $167.59   $167.60   $167.60  
  Purchase #2 $47.42   13.765%   $53.9474   $53.95   $53.95   $53.90  
  Purchase #3 $248.39   11.333%   $276.54   $276.54   $276.55   $276.50  
  Purchase #4 $26.51   7.115%   $28.3962   $28.40   $28.40   $28.40  
  Purchase #5 $63.99   4.474%   $66.8529   $66.85   $66.85   $66.90  
  Purchase #6 $169.57   4.476%   $177.16   $177.16   $177.15   $177.20  
  Purchase #7 $178.67   11.782%   $199.7209   $199.72   $199.70   $199.70  
  7 purchase totals = $887.09       $970.2085   $970.21   $970.20   $970.20