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 $110.75   13.764%   $125.9936   $125.99   $126.00   $126.00  
  Purchase #2 $95.83   6.480%   $102.0398   $102.04   $102.05   $102.00  
  Purchase #3 $125.31   8.750%   $136.2746   $136.27   $136.25   $136.30  
  Purchase #4 $200.80   7.344%   $215.5468   $215.55   $215.55   $215.50  
  Purchase #5 $50.57   10.807%   $56.0351   $56.04   $56.05   $56.00  
  Purchase #6 $152.45   5.241%   $160.4399   $160.44   $160.45   $160.40  
  Purchase #7 $119.49   12.244%   $134.1204   $134.12   $134.10   $134.10  
  7 purchase totals = $855.20       $930.4502   $930.45   $930.45   $930.30