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 $174.47   12.526%   $196.3241   $196.32   $196.30   $196.30  
  Purchase #2 $168.64   11.395%   $187.8565   $187.86   $187.85   $187.90  
  Purchase #3 $88.79   10.549%   $98.1565   $98.16   $98.15   $98.20  
  Purchase #4 $26.57   12.106%   $29.7866   $29.79   $29.80   $29.80  
  Purchase #5 $159.97   10.848%   $177.3235   $177.32   $177.30   $177.30  
  Purchase #6 $250.95   9.242%   $274.1428   $274.14   $274.15   $274.10  
  Purchase #7 $231.79   3.310%   $239.4622   $239.46   $239.45   $239.50  
  7 purchase totals = $1,101.18       $1,203.0522   $1,203.05   $1,203.00   $1,203.10