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 $52.81   6.522%   $56.2543   $56.25   $56.25   $56.30  
  Purchase #2 $182.42   13.767%   $207.5338   $207.53   $207.55   $207.50  
  Purchase #3 $195.81   3.198%   $202.072   $202.07   $202.05   $202.10  
  Purchase #4 $211.98   5.187%   $222.9754   $222.98   $223.00   $223.00  
  Purchase #5 $181.46   6.393%   $193.0607   $193.06   $193.05   $193.10  
  Purchase #6 $22.42   8.174%   $24.2526   $24.25   $24.25   $24.30  
  Purchase #7 $115.42   8.281%   $124.9779   $124.98   $125.00   $125.00  
  7 purchase totals = $962.32       $1,031.1267   $1,031.12   $1,031.15   $1,031.30