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 $50.83   11.316%   $56.5819   $56.58   $56.60   $56.60  
  Purchase #2 $83.35   4.812%   $87.3608   $87.36   $87.35   $87.40  
  Purchase #3 $74.29   11.194%   $82.606   $82.61   $82.60   $82.60  
  Purchase #4 $186.73   7.597%   $200.9159   $200.92   $200.90   $200.90  
  Purchase #5 $189.72   6.349%   $201.7653   $201.77   $201.75   $201.80  
  Purchase #6 $142.25   10.370%   $157.0013   $157.00   $157.00   $157.00  
  Purchase #7 $230.37   11.126%   $256.001   $256.00   $256.00   $256.00  
  7 purchase totals = $957.54       $1,042.2322   $1,042.24   $1,042.20   $1,042.30