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 $124.61   11.230%   $138.6037   $138.60   $138.60   $138.60  
  Purchase #2 $186.58   10.128%   $205.4768   $205.48   $205.50   $205.50  
  Purchase #3 $95.50   12.652%   $107.5827   $107.58   $107.60   $107.60  
  Purchase #4 $136.39   7.644%   $146.8157   $146.82   $146.80   $146.80  
  Purchase #5 $168.77   9.733%   $185.1964   $185.20   $185.20   $185.20  
  Purchase #6 $44.38   13.808%   $50.508   $50.51   $50.50   $50.50  
  Purchase #7 $33.82   9.366%   $36.9876   $36.99   $37.00   $37.00  
  7 purchase totals = $790.05       $871.1709   $871.18   $871.20   $871.20