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 $84.80   10.856%   $94.0059   $94.01   $94.00   $94.00  
  Purchase #2 $191.38   8.238%   $207.1459   $207.15   $207.15   $207.10  
  Purchase #3 $140.99   10.111%   $155.2455   $155.25   $155.25   $155.20  
  Purchase #4 $231.44   11.239%   $257.4515   $257.45   $257.45   $257.50  
  Purchase #5 $200.38   12.812%   $226.0527   $226.05   $226.05   $226.10  
  Purchase #6 $112.87   13.325%   $127.9099   $127.91   $127.90   $127.90  
  Purchase #7 $34.41   3.329%   $35.5555   $35.56   $35.55   $35.60  
  7 purchase totals = $996.27       $1,103.3669   $1,103.38   $1,103.35   $1,103.40