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 $241.36   4.642%   $252.5639   $252.56   $252.55   $252.60  
  Purchase #2 $200.53   6.328%   $213.2195   $213.22   $213.20   $213.20  
  Purchase #3 $164.25   8.131%   $177.6052   $177.61   $177.60   $177.60  
  Purchase #4 $46.47   4.695%   $48.6518   $48.65   $48.65   $48.70  
  Purchase #5 $240.41   3.159%   $248.0046   $248.00   $248.00   $248.00  
  Purchase #6 $178.91   8.570%   $194.2426   $194.24   $194.25   $194.20  
  Purchase #7 $209.31   13.531%   $237.6317   $237.63   $237.65   $237.60  
  7 purchase totals = $1,281.24       $1,371.9193   $1,371.91   $1,371.90   $1,371.90