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 $118.76   6.105%   $126.0103   $126.01   $126.00   $126.00  
  Purchase #2 $151.80   12.727%   $171.1196   $171.12   $171.10   $171.10  
  Purchase #3 $118.73   12.590%   $133.6781   $133.68   $133.70   $133.70  
  Purchase #4 $203.77   13.320%   $230.9122   $230.91   $230.90   $230.90  
  Purchase #5 $13.59   8.864%   $14.7946   $14.79   $14.80   $14.80  
  Purchase #6 $237.88   6.584%   $253.542   $253.54   $253.55   $253.50  
  Purchase #7 $72.38   9.203%   $79.0411   $79.04   $79.05   $79.00  
  7 purchase totals = $916.91       $1,009.0979   $1,009.09   $1,009.10   $1,009.00