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 $204.67   12.705%   $230.6733   $230.67   $230.65   $230.70  
  Purchase #2 $249.82   3.516%   $258.6037   $258.60   $258.60   $258.60  
  Purchase #3 $192.38   6.309%   $204.5173   $204.52   $204.50   $204.50  
  Purchase #4 $121.58   4.837%   $127.4608   $127.46   $127.45   $127.50  
  Purchase #5 $165.69   3.371%   $171.2754   $171.28   $171.30   $171.30  
  Purchase #6 $238.65   11.860%   $266.9539   $266.95   $266.95   $267.00  
  Purchase #7 $84.25   11.625%   $94.0441   $94.04   $94.05   $94.00  
  7 purchase totals = $1,257.04       $1,353.5285   $1,353.52   $1,353.50   $1,353.60