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 $168.58   8.303%   $182.5772   $182.58   $182.60   $182.60  
  Purchase #2 $209.75   6.154%   $222.658   $222.66   $222.65   $222.70  
  Purchase #3 $43.64   12.502%   $49.0959   $49.10   $49.10   $49.10  
  Purchase #4 $115.30   9.345%   $126.0748   $126.07   $126.05   $126.10  
  Purchase #5 $224.71   6.699%   $239.7633   $239.76   $239.75   $239.80  
  Purchase #6 $57.64   9.246%   $62.9694   $62.97   $62.95   $63.00  
  Purchase #7 $39.63   8.345%   $42.9371   $42.94   $42.95   $42.90  
  7 purchase totals = $859.25       $926.0757   $926.08   $926.05   $926.20