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 $83.68   11.172%   $93.0287   $93.03   $93.05   $93.00  
  Purchase #2 $183.68   13.590%   $208.6421   $208.64   $208.65   $208.60  
  Purchase #3 $129.34   11.182%   $143.8028   $143.80   $143.80   $143.80  
  Purchase #4 $239.66   11.273%   $266.6769   $266.68   $266.70   $266.70  
  Purchase #5 $139.98   3.545%   $144.9423   $144.94   $144.95   $144.90  
  Purchase #6 $200.87   5.618%   $212.1549   $212.15   $212.15   $212.20  
  Purchase #7 $89.90   6.738%   $95.9575   $95.96   $95.95   $96.00  
  7 purchase totals = $1,067.11       $1,165.2052   $1,165.20   $1,165.25   $1,165.20