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 $63.95   8.742%   $69.5405   $69.54   $69.55   $69.50  
  Purchase #2 $42.90   8.217%   $46.4251   $46.43   $46.45   $46.40  
  Purchase #3 $65.46   5.728%   $69.2095   $69.21   $69.20   $69.20  
  Purchase #4 $197.33   9.594%   $216.2618   $216.26   $216.25   $216.30  
  Purchase #5 $15.81   11.108%   $17.5662   $17.57   $17.55   $17.60  
  Purchase #6 $68.76   4.150%   $71.6135   $71.61   $71.60   $71.60  
  Purchase #7 $151.25   5.547%   $159.6398   $159.64   $159.65   $159.60  
  7 purchase totals = $605.46       $650.2564   $650.26   $650.25   $650.20