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 $53.33   6.408%   $56.7474   $56.75   $56.75   $56.70  
  Purchase #2 $200.34   3.422%   $207.1956   $207.20   $207.20   $207.20  
  Purchase #3 $31.93   9.759%   $35.046   $35.05   $35.05   $35.00  
  Purchase #4 $189.61   9.414%   $207.4599   $207.46   $207.45   $207.50  
  Purchase #5 $115.86   10.770%   $128.3381   $128.34   $128.35   $128.30  
  Purchase #6 $202.83   11.309%   $225.768   $225.77   $225.75   $225.80  
  Purchase #7 $124.93   10.832%   $138.4624   $138.46   $138.45   $138.50  
  7 purchase totals = $918.83       $999.0174   $999.03   $999.00   $999.00