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 $208.37   11.174%   $231.6533   $231.65   $231.65   $231.70  
  Purchase #2 $222.33   9.421%   $243.2757   $243.28   $243.30   $243.30  
  Purchase #3 $82.68   13.651%   $93.9666   $93.97   $93.95   $94.00  
  Purchase #4 $174.73   4.552%   $182.6837   $182.68   $182.70   $182.70  
  Purchase #5 $30.69   5.376%   $32.3399   $32.34   $32.35   $32.30  
  Purchase #6 $235.84   6.106%   $250.2404   $250.24   $250.25   $250.20  
  Purchase #7 $220.36   3.194%   $227.3983   $227.40   $227.40   $227.40  
  7 purchase totals = $1,175.00       $1,261.5579   $1,261.56   $1,261.60   $1,261.60