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 $212.99   13.339%   $241.4007   $241.40   $241.40   $241.40  
  Purchase #2 $36.38   4.554%   $38.0367   $38.04   $38.05   $38.00  
  Purchase #3 $151.70   8.680%   $164.8676   $164.87   $164.85   $164.90  
  Purchase #4 $112.58   13.778%   $128.0913   $128.09   $128.10   $128.10  
  Purchase #5 $26.44   4.360%   $27.5928   $27.59   $27.60   $27.60  
  Purchase #6 $43.58   8.767%   $47.4007   $47.40   $47.40   $47.40  
  Purchase #7 $49.33   9.849%   $54.1885   $54.19   $54.20   $54.20  
  7 purchase totals = $633.00       $701.5783   $701.58   $701.60   $701.60