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 $46.84   3.210%   $48.3436   $48.34   $48.35   $48.30  
  Purchase #2 $43.70   5.685%   $46.1843   $46.18   $46.20   $46.20  
  Purchase #3 $125.99   8.169%   $136.2821   $136.28   $136.30   $136.30  
  Purchase #4 $91.51   3.338%   $94.5646   $94.56   $94.55   $94.60  
  Purchase #5 $81.99   11.365%   $91.3082   $91.31   $91.30   $91.30  
  Purchase #6 $200.40   3.846%   $208.1074   $208.11   $208.10   $208.10  
  Purchase #7 $113.57   13.825%   $129.2711   $129.27   $129.25   $129.30  
  7 purchase totals = $704.00       $754.0613   $754.05   $754.05   $754.10