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 $229.32   5.487%   $241.9028   $241.90   $241.90   $241.90  
  Purchase #2 $131.44   12.786%   $148.2459   $148.25   $148.25   $148.20  
  Purchase #3 $70.90   5.225%   $74.6045   $74.60   $74.60   $74.60  
  Purchase #4 $230.87   13.733%   $262.5754   $262.58   $262.60   $262.60  
  Purchase #5 $37.91   5.714%   $40.0762   $40.08   $40.10   $40.10  
  Purchase #6 $83.87   8.589%   $91.0736   $91.07   $91.05   $91.10  
  Purchase #7 $150.61   11.720%   $168.2615   $168.26   $168.25   $168.30  
  7 purchase totals = $934.92       $1,026.7399   $1,026.74   $1,026.75   $1,026.80