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 $239.34   9.698%   $262.5512   $262.55   $262.55   $262.60  
  Purchase #2 $93.57   13.212%   $105.9325   $105.93   $105.95   $105.90  
  Purchase #3 $124.29   4.150%   $129.448   $129.45   $129.45   $129.40  
  Purchase #4 $27.31   8.231%   $29.5579   $29.56   $29.55   $29.60  
  Purchase #5 $162.45   8.827%   $176.7895   $176.79   $176.80   $176.80  
  Purchase #6 $228.56   5.593%   $241.3434   $241.34   $241.35   $241.30  
  Purchase #7 $100.39   13.614%   $114.0571   $114.06   $114.05   $114.10  
  7 purchase totals = $975.91       $1,059.6796   $1,059.68   $1,059.70   $1,059.70