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 $236.96   13.424%   $268.7695   $268.77   $268.75   $268.80  
  Purchase #2 $54.74   9.741%   $60.0722   $60.07   $60.05   $60.10  
  Purchase #3 $160.40   5.638%   $169.4434   $169.44   $169.45   $169.40  
  Purchase #4 $248.74   4.466%   $259.8487   $259.85   $259.85   $259.80  
  Purchase #5 $115.76   12.798%   $130.575   $130.58   $130.60   $130.60  
  Purchase #6 $160.29   3.647%   $166.1358   $166.14   $166.15   $166.10  
  Purchase #7 $226.83   9.375%   $248.0953   $248.10   $248.10   $248.10  
  7 purchase totals = $1,203.72       $1,302.9399   $1,302.95   $1,302.95   $1,302.90