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 $118.69   5.553%   $125.2809   $125.28   $125.30   $125.30  
  Purchase #2 $141.62   10.402%   $156.3513   $156.35   $156.35   $156.40  
  Purchase #3 $56.57   9.602%   $62.0019   $62.00   $62.00   $62.00  
  Purchase #4 $63.73   6.533%   $67.8935   $67.89   $67.90   $67.90  
  Purchase #5 $181.35   11.509%   $202.2216   $202.22   $202.20   $202.20  
  Purchase #6 $156.50   3.612%   $162.1528   $162.15   $162.15   $162.20  
  Purchase #7 $26.35   3.411%   $27.2488   $27.25   $27.25   $27.20  
  7 purchase totals = $744.81       $803.1508   $803.14   $803.15   $803.20