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 $52.97   13.668%   $60.2099   $60.21   $60.20   $60.20  
  Purchase #2 $248.60   11.127%   $276.2617   $276.26   $276.25   $276.30  
  Purchase #3 $38.42   13.597%   $43.644   $43.64   $43.65   $43.60  
  Purchase #4 $90.50   13.752%   $102.9456   $102.95   $102.95   $102.90  
  Purchase #5 $157.27   3.688%   $163.0701   $163.07   $163.05   $163.10  
  Purchase #6 $225.85   7.413%   $242.5923   $242.59   $242.60   $242.60  
  Purchase #7 $40.93   8.700%   $44.4909   $44.49   $44.50   $44.50  
  7 purchase totals = $854.54       $933.2145   $933.21   $933.20   $933.20