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 $54.86   9.422%   $60.0289   $60.03   $60.05   $60.00  
  Purchase #2 $240.60   5.350%   $253.4721   $253.47   $253.45   $253.50  
  Purchase #3 $77.31   8.237%   $83.678   $83.68   $83.70   $83.70  
  Purchase #4 $206.76   5.793%   $218.7376   $218.74   $218.75   $218.70  
  Purchase #5 $59.69   7.593%   $64.2223   $64.22   $64.20   $64.20  
  Purchase #6 $102.44   10.384%   $113.0774   $113.08   $113.10   $113.10  
  Purchase #7 $151.25   4.423%   $157.9398   $157.94   $157.95   $157.90  
  7 purchase totals = $892.91       $951.1561   $951.16   $951.20   $951.10