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 $163.79   13.278%   $185.538   $185.54   $185.55   $185.50  
  Purchase #2 $175.56   9.745%   $192.6683   $192.67   $192.65   $192.70  
  Purchase #3 $225.89   7.411%   $242.6307   $242.63   $242.65   $242.60  
  Purchase #4 $75.61   13.716%   $85.9807   $85.98   $86.00   $86.00  
  Purchase #5 $154.79   7.873%   $166.9766   $166.98   $167.00   $167.00  
  Purchase #6 $94.99   8.808%   $103.3567   $103.36   $103.35   $103.40  
  Purchase #7 $202.69   9.803%   $222.5597   $222.56   $222.55   $222.60  
  7 purchase totals = $1,093.32       $1,199.7107   $1,199.72   $1,199.75   $1,199.80