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 $168.40   8.102%   $182.0438   $182.04   $182.05   $182.00  
  Purchase #2 $246.34   8.206%   $266.5547   $266.55   $266.55   $266.60  
  Purchase #3 $179.55   3.413%   $185.678   $185.68   $185.70   $185.70  
  Purchase #4 $44.81   7.386%   $48.1197   $48.12   $48.10   $48.10  
  Purchase #5 $208.64   6.777%   $222.7795   $222.78   $222.80   $222.80  
  Purchase #6 $207.93   3.420%   $215.0412   $215.04   $215.05   $215.00  
  Purchase #7 $84.73   9.868%   $93.0912   $93.09   $93.10   $93.10  
  7 purchase totals = $1,140.40       $1,213.3081   $1,213.30   $1,213.35   $1,213.30