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 $10.30   10.664%   $11.3984   $11.40   $11.40   $11.40  
  Purchase #2 $129.63   10.304%   $142.9871   $142.99   $143.00   $143.00  
  Purchase #3 $29.61   6.169%   $31.4366   $31.44   $31.45   $31.40  
  Purchase #4 $60.96   13.482%   $69.1786   $69.18   $69.20   $69.20  
  Purchase #5 $49.55   11.141%   $55.0704   $55.07   $55.05   $55.10  
  Purchase #6 $100.48   7.874%   $108.3918   $108.39   $108.40   $108.40  
  Purchase #7 $90.55   9.840%   $99.4601   $99.46   $99.45   $99.50  
  7 purchase totals = $471.08       $517.9230   $517.93   $517.95   $518.00