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 $244.68   5.549%   $258.2573   $258.26   $258.25   $258.30  
  Purchase #2 $243.43   7.639%   $262.0256   $262.03   $262.05   $262.00  
  Purchase #3 $218.29   6.652%   $232.8107   $232.81   $232.80   $232.80  
  Purchase #4 $25.36   3.163%   $26.1621   $26.16   $26.15   $26.20  
  Purchase #5 $29.51   5.393%   $31.1015   $31.10   $31.10   $31.10  
  Purchase #6 $136.92   13.551%   $155.474   $155.47   $155.45   $155.50  
  Purchase #7 $71.25   11.499%   $79.443   $79.44   $79.45   $79.40  
  7 purchase totals = $969.44       $1,045.2742   $1,045.27   $1,045.25   $1,045.30