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 $210.64   4.449%   $220.0114   $220.01   $220.00   $220.00  
  Purchase #2 $23.61   11.112%   $26.2335   $26.23   $26.25   $26.20  
  Purchase #3 $88.88   12.469%   $99.9624   $99.96   $99.95   $100.00  
  Purchase #4 $15.95   12.458%   $17.9371   $17.94   $17.95   $17.90  
  Purchase #5 $59.36   13.376%   $67.3   $67.30   $67.30   $67.30  
  Purchase #6 $29.33   5.481%   $30.9376   $30.94   $30.95   $30.90  
  Purchase #7 $155.83   7.264%   $167.1495   $167.15   $167.15   $167.10  
  7 purchase totals = $583.60       $629.5315   $629.53   $629.55   $629.40