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 $242.49   8.440%   $262.9562   $262.96   $262.95   $263.00  
  Purchase #2 $156.83   12.564%   $176.5341   $176.53   $176.55   $176.50  
  Purchase #3 $161.69   7.654%   $174.0658   $174.07   $174.05   $174.10  
  Purchase #4 $37.45   4.311%   $39.0645   $39.06   $39.05   $39.10  
  Purchase #5 $218.55   10.690%   $241.913   $241.91   $241.90   $241.90  
  Purchase #6 $25.80   6.188%   $27.3965   $27.40   $27.40   $27.40  
  Purchase #7 $27.30   11.842%   $30.5329   $30.53   $30.55   $30.50  
  7 purchase totals = $870.11       $952.4630   $952.46   $952.45   $952.50