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 $165.66   13.109%   $187.3764   $187.38   $187.40   $187.40  
  Purchase #2 $109.58   4.799%   $114.8387   $114.84   $114.85   $114.80  
  Purchase #3 $57.94   13.592%   $65.8152   $65.82   $65.80   $65.80  
  Purchase #4 $218.82   13.620%   $248.6233   $248.62   $248.60   $248.60  
  Purchase #5 $162.56   4.175%   $169.3469   $169.35   $169.35   $169.30  
  Purchase #6 $58.76   8.614%   $63.8216   $63.82   $63.80   $63.80  
  Purchase #7 $209.56   8.214%   $226.7733   $226.77   $226.75   $226.80  
  7 purchase totals = $982.88       $1,076.5954   $1,076.60   $1,076.55   $1,076.50