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 $213.41   10.624%   $236.0827   $236.08   $236.10   $236.10  
  Purchase #2 $52.51   7.413%   $56.4026   $56.40   $56.40   $56.40  
  Purchase #3 $26.72   12.464%   $30.0504   $30.05   $30.05   $30.10  
  Purchase #4 $107.94   12.540%   $121.4757   $121.48   $121.50   $121.50  
  Purchase #5 $184.39   6.253%   $195.9199   $195.92   $195.90   $195.90  
  Purchase #6 $105.39   8.375%   $114.2164   $114.22   $114.20   $114.20  
  Purchase #7 $163.76   13.753%   $186.2819   $186.28   $186.30   $186.30  
  7 purchase totals = $854.12       $940.4296   $940.43   $940.45   $940.50