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 $184.71   9.545%   $202.3406   $202.34   $202.35   $202.30  
  Purchase #2 $41.73   10.378%   $46.0607   $46.06   $46.05   $46.10  
  Purchase #3 $185.98   11.726%   $207.788   $207.79   $207.80   $207.80  
  Purchase #4 $96.53   12.531%   $108.6262   $108.63   $108.65   $108.60  
  Purchase #5 $110.37   4.821%   $115.6909   $115.69   $115.70   $115.70  
  Purchase #6 $242.70   9.370%   $265.441   $265.44   $265.45   $265.40  
  Purchase #7 $12.66   10.215%   $13.9532   $13.95   $13.95   $14.00  
  7 purchase totals = $874.68       $959.9006   $959.90   $959.95   $959.90