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 $191.88   6.266%   $203.9032   $203.90   $203.90   $203.90  
  Purchase #2 $239.59   11.291%   $266.6421   $266.64   $266.65   $266.60  
  Purchase #3 $177.25   12.111%   $198.7167   $198.72   $198.70   $198.70  
  Purchase #4 $212.84   9.163%   $232.3425   $232.34   $232.35   $232.30  
  Purchase #5 $74.86   4.224%   $78.0221   $78.02   $78.00   $78.00  
  Purchase #6 $49.33   5.499%   $52.0427   $52.04   $52.05   $52.00  
  Purchase #7 $63.33   13.838%   $72.0936   $72.09   $72.10   $72.10  
  7 purchase totals = $1,009.08       $1,103.7629   $1,103.75   $1,103.75   $1,103.60