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 $56.97   7.157%   $61.0473   $61.05   $61.05   $61.00  
  Purchase #2 $183.93   13.282%   $208.3596   $208.36   $208.35   $208.40  
  Purchase #3 $144.46   9.438%   $158.0941   $158.09   $158.10   $158.10  
  Purchase #4 $58.33   10.722%   $64.5841   $64.58   $64.60   $64.60  
  Purchase #5 $5.95   5.293%   $6.2649   $6.26   $6.25   $6.30  
  Purchase #6 $215.30   13.247%   $243.8208   $243.82   $243.80   $243.80  
  Purchase #7 $154.27   13.338%   $174.8465   $174.85   $174.85   $174.80  
  7 purchase totals = $819.21       $917.0173   $917.01   $917.00   $917.00