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 $50.49   11.238%   $56.1641   $56.16   $56.15   $56.20  
  Purchase #2 $191.79   8.741%   $208.5544   $208.55   $208.55   $208.60  
  Purchase #3 $89.99   4.511%   $94.0494   $94.05   $94.05   $94.00  
  Purchase #4 $180.86   9.229%   $197.5516   $197.55   $197.55   $197.60  
  Purchase #5 $41.42   12.484%   $46.5909   $46.59   $46.60   $46.60  
  Purchase #6 $166.81   11.231%   $185.5444   $185.54   $185.55   $185.50  
  Purchase #7 $221.57   9.830%   $243.3503   $243.35   $243.35   $243.40  
  7 purchase totals = $942.93       $1,031.8051   $1,031.79   $1,031.80   $1,031.90