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 $241.47   11.393%   $268.9807   $268.98   $269.00   $269.00  
  Purchase #2 $196.68   3.371%   $203.3101   $203.31   $203.30   $203.30  
  Purchase #3 $62.81   10.582%   $69.4566   $69.46   $69.45   $69.50  
  Purchase #4 $101.50   13.124%   $114.8209   $114.82   $114.80   $114.80  
  Purchase #5 $202.47   11.639%   $226.0355   $226.04   $226.05   $226.00  
  Purchase #6 $199.57   3.226%   $206.0081   $206.01   $206.00   $206.00  
  Purchase #7 $75.60   6.662%   $80.6365   $80.64   $80.65   $80.60  
  7 purchase totals = $1,080.10       $1,169.2484   $1,169.26   $1,169.25   $1,169.20