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 $229.52   5.291%   $241.6639   $241.66   $241.65   $241.70  
  Purchase #2 $61.93   3.327%   $63.9904   $63.99   $64.00   $64.00  
  Purchase #3 $135.65   13.434%   $153.8732   $153.87   $153.85   $153.90  
  Purchase #4 $239.48   9.227%   $261.5768   $261.58   $261.60   $261.60  
  Purchase #5 $76.78   12.739%   $86.561   $86.56   $86.55   $86.60  
  Purchase #6 $245.91   5.233%   $258.7785   $258.78   $258.80   $258.80  
  Purchase #7 $129.37   9.236%   $141.3186   $141.32   $141.30   $141.30  
  7 purchase totals = $1,118.64       $1,207.7624   $1,207.76   $1,207.75   $1,207.90