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 $248.69   5.583%   $262.5744   $262.57   $262.55   $262.60  
  Purchase #2 $186.81   8.639%   $202.9485   $202.95   $202.95   $202.90  
  Purchase #3 $219.93   6.433%   $234.0781   $234.08   $234.10   $234.10  
  Purchase #4 $167.75   11.609%   $187.2241   $187.22   $187.20   $187.20  
  Purchase #5 $61.35   6.408%   $65.2813   $65.28   $65.30   $65.30  
  Purchase #6 $148.82   5.169%   $156.5125   $156.51   $156.50   $156.50  
  Purchase #7 $187.50   4.623%   $196.1681   $196.17   $196.15   $196.20  
  7 purchase totals = $1,220.85       $1,304.7870   $1,304.78   $1,304.75   $1,304.80