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 $187.45   12.644%   $211.1512   $211.15   $211.15   $211.20  
  Purchase #2 $154.67   3.218%   $159.6473   $159.65   $159.65   $159.60  
  Purchase #3 $248.34   13.288%   $281.3394   $281.34   $281.35   $281.30  
  Purchase #4 $161.95   13.473%   $183.7695   $183.77   $183.75   $183.80  
  Purchase #5 $105.99   8.136%   $114.6133   $114.61   $114.60   $114.60  
  Purchase #6 $65.73   11.871%   $73.5328   $73.53   $73.55   $73.50  
  Purchase #7 $71.62   3.810%   $74.3487   $74.35   $74.35   $74.30  
  7 purchase totals = $995.75       $1,098.4022   $1,098.40   $1,098.40   $1,098.30