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 $233.66   11.710%   $261.0216   $261.02   $261.00   $261.00  
  Purchase #2 $205.43   7.104%   $220.0237   $220.02   $220.00   $220.00  
  Purchase #3 $46.73   5.627%   $49.3595   $49.36   $49.35   $49.40  
  Purchase #4 $75.79   3.242%   $78.2471   $78.25   $78.25   $78.20  
  Purchase #5 $164.52   10.689%   $182.1055   $182.11   $182.10   $182.10  
  Purchase #6 $105.52   9.139%   $115.1635   $115.16   $115.15   $115.20  
  Purchase #7 $135.58   6.713%   $144.6815   $144.68   $144.70   $144.70  
  7 purchase totals = $967.23       $1,050.6024   $1,050.60   $1,050.55   $1,050.60