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 $54.28   12.392%   $61.0064   $61.01   $61.00   $61.00  
  Purchase #2 $221.83   12.615%   $249.8139   $249.81   $249.80   $249.80  
  Purchase #3 $164.34   10.798%   $182.0854   $182.09   $182.10   $182.10  
  Purchase #4 $216.73   13.180%   $245.295   $245.30   $245.30   $245.30  
  Purchase #5 $67.58   3.299%   $69.8095   $69.81   $69.80   $69.80  
  Purchase #6 $60.73   11.653%   $67.8069   $67.81   $67.80   $67.80  
  Purchase #7 $100.69   3.532%   $104.2464   $104.25   $104.25   $104.20  
  7 purchase totals = $886.18       $980.0635   $980.08   $980.05   $980.00