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 $178.25   13.346%   $202.0392   $202.04   $202.05   $202.00  
  Purchase #2 $195.97   13.158%   $221.7557   $221.76   $221.75   $221.80  
  Purchase #3 $32.37   11.382%   $36.0544   $36.05   $36.05   $36.10  
  Purchase #4 $76.67   7.106%   $82.1182   $82.12   $82.10   $82.10  
  Purchase #5 $36.90   13.122%   $41.742   $41.74   $41.75   $41.70  
  Purchase #6 $140.48   9.301%   $153.546   $153.55   $153.55   $153.50  
  Purchase #7 $55.74   8.160%   $60.2884   $60.29   $60.30   $60.30  
  7 purchase totals = $716.38       $797.5439   $797.55   $797.55   $797.50