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 $164.64   8.719%   $178.995   $179.00   $179.00   $179.00  
  Purchase #2 $71.38   4.805%   $74.8098   $74.81   $74.80   $74.80  
  Purchase #3 $17.53   9.213%   $19.145   $19.15   $19.15   $19.10  
  Purchase #4 $73.50   4.471%   $76.7862   $76.79   $76.80   $76.80  
  Purchase #5 $118.90   7.225%   $127.4905   $127.49   $127.50   $127.50  
  Purchase #6 $130.74   8.683%   $142.0922   $142.09   $142.10   $142.10  
  Purchase #7 $11.39   5.424%   $12.0078   $12.01   $12.00   $12.00  
  7 purchase totals = $588.08       $631.3265   $631.34   $631.35   $631.30