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 $238.66   10.857%   $264.5713   $264.57   $264.55   $264.60  
  Purchase #2 $161.39   9.445%   $176.6333   $176.63   $176.65   $176.60  
  Purchase #3 $33.50   4.193%   $34.9047   $34.90   $34.90   $34.90  
  Purchase #4 $174.37   8.208%   $188.6823   $188.68   $188.70   $188.70  
  Purchase #5 $47.91   10.503%   $52.942   $52.94   $52.95   $52.90  
  Purchase #6 $231.80   9.812%   $254.5442   $254.54   $254.55   $254.50  
  Purchase #7 $69.68   10.244%   $76.818   $76.82   $76.80   $76.80  
  7 purchase totals = $957.31       $1,049.0958   $1,049.08   $1,049.10   $1,049.00