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 $140.43   12.849%   $158.4739   $158.47   $158.45   $158.50  
  Purchase #2 $180.43   9.730%   $197.9858   $197.99   $198.00   $198.00  
  Purchase #3 $130.93   11.112%   $145.4789   $145.48   $145.50   $145.50  
  Purchase #4 $233.85   13.149%   $264.5989   $264.60   $264.60   $264.60  
  Purchase #5 $103.67   9.597%   $113.6192   $113.62   $113.60   $113.60  
  Purchase #6 $43.40   7.653%   $46.7214   $46.72   $46.70   $46.70  
  Purchase #7 $197.27   5.777%   $208.6663   $208.67   $208.65   $208.70  
  7 purchase totals = $1,029.98       $1,135.5444   $1,135.55   $1,135.50   $1,135.60