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 $63.52   12.422%   $71.4105   $71.41   $71.40   $71.40  
  Purchase #2 $244.72   6.868%   $261.5274   $261.53   $261.55   $261.50  
  Purchase #3 $244.41   4.105%   $254.443   $254.44   $254.45   $254.40  
  Purchase #4 $192.87   9.582%   $211.3508   $211.35   $211.35   $211.40  
  Purchase #5 $45.99   9.155%   $50.2004   $50.20   $50.20   $50.20  
  Purchase #6 $249.76   6.331%   $265.5723   $265.57   $265.55   $265.60  
  Purchase #7 $215.50   10.364%   $237.8344   $237.83   $237.85   $237.80  
  7 purchase totals = $1,256.77       $1,352.3388   $1,352.33   $1,352.35   $1,352.30