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 $97.65   13.721%   $111.0486   $111.05   $111.05   $111.00  
  Purchase #2 $118.54   6.109%   $125.7816   $125.78   $125.80   $125.80  
  Purchase #3 $55.69   9.553%   $61.0101   $61.01   $61.00   $61.00  
  Purchase #4 $58.41   3.828%   $60.6459   $60.65   $60.65   $60.60  
  Purchase #5 $88.66   10.769%   $98.2078   $98.21   $98.20   $98.20  
  Purchase #6 $226.81   5.661%   $239.6497   $239.65   $239.65   $239.60  
  Purchase #7 $95.78   10.788%   $106.1127   $106.11   $106.10   $106.10  
  7 purchase totals = $741.54       $802.4564   $802.46   $802.45   $802.30