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 $64.28   4.234%   $67.0016   $67.00   $67.00   $67.00  
  Purchase #2 $112.34   8.613%   $122.0158   $122.02   $122.00   $122.00  
  Purchase #3 $54.55   6.184%   $57.9234   $57.92   $57.90   $57.90  
  Purchase #4 $136.61   7.766%   $147.2191   $147.22   $147.20   $147.20  
  Purchase #5 $226.49   3.582%   $234.6029   $234.60   $234.60   $234.60  
  Purchase #6 $214.83   5.556%   $226.766   $226.77   $226.75   $226.80  
  Purchase #7 $139.67   8.854%   $152.0364   $152.04   $152.05   $152.00  
  7 purchase totals = $948.77       $1,007.5652   $1,007.57   $1,007.50   $1,007.50