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 $215.63   13.626%   $245.0117   $245.01   $245.00   $245.00  
  Purchase #2 $237.76   7.651%   $255.951   $255.95   $255.95   $256.00  
  Purchase #3 $196.52   12.269%   $220.631   $220.63   $220.65   $220.60  
  Purchase #4 $92.41   6.118%   $98.0636   $98.06   $98.05   $98.10  
  Purchase #5 $44.89   11.354%   $49.9868   $49.99   $50.00   $50.00  
  Purchase #6 $74.59   13.354%   $84.5507   $84.55   $84.55   $84.60  
  Purchase #7 $247.85   12.520%   $278.8808   $278.88   $278.90   $278.90  
  7 purchase totals = $1,109.65       $1,233.0756   $1,233.07   $1,233.10   $1,233.20