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 $240.33   4.861%   $252.0124   $252.01   $252.00   $252.00  
  Purchase #2 $55.57   3.207%   $57.3521   $57.35   $57.35   $57.40  
  Purchase #3 $227.75   9.176%   $248.6483   $248.65   $248.65   $248.60  
  Purchase #4 $122.34   10.272%   $134.9068   $134.91   $134.90   $134.90  
  Purchase #5 $226.63   13.328%   $256.8352   $256.84   $256.85   $256.80  
  Purchase #6 $169.84   6.163%   $180.3072   $180.31   $180.30   $180.30  
  Purchase #7 $126.83   3.494%   $131.2614   $131.26   $131.25   $131.30  
  7 purchase totals = $1,169.29       $1,261.3234   $1,261.33   $1,261.30   $1,261.30