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 $217.98   12.520%   $245.2711   $245.27   $245.25   $245.30  
  Purchase #2 $238.62   12.160%   $267.6362   $267.64   $267.65   $267.60  
  Purchase #3 $210.62   4.557%   $220.218   $220.22   $220.20   $220.20  
  Purchase #4 $210.47   10.211%   $231.9611   $231.96   $231.95   $232.00  
  Purchase #5 $211.72   7.261%   $227.093   $227.09   $227.10   $227.10  
  Purchase #6 $90.90   8.290%   $98.4356   $98.44   $98.45   $98.40  
  Purchase #7 $50.31   10.246%   $55.4648   $55.46   $55.45   $55.50  
  7 purchase totals = $1,230.62       $1,346.0798   $1,346.08   $1,346.05   $1,346.10