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 $58.94   12.332%   $66.2085   $66.21   $66.20   $66.20  
  Purchase #2 $82.78   10.650%   $91.5961   $91.60   $91.60   $91.60  
  Purchase #3 $27.37   8.714%   $29.755   $29.76   $29.75   $29.80  
  Purchase #4 $72.48   5.793%   $76.6788   $76.68   $76.70   $76.70  
  Purchase #5 $145.72   5.780%   $154.1426   $154.14   $154.15   $154.10  
  Purchase #6 $225.49   5.284%   $237.4049   $237.40   $237.40   $237.40  
  Purchase #7 $115.69   12.773%   $130.4671   $130.47   $130.45   $130.50  
  7 purchase totals = $728.47       $786.2530   $786.26   $786.25   $786.30