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 $246.82   5.798%   $261.1306   $261.13   $261.15   $261.10  
  Purchase #2 $93.99   13.439%   $106.6213   $106.62   $106.60   $106.60  
  Purchase #3 $202.67   7.342%   $217.55   $217.55   $217.55   $217.60  
  Purchase #4 $149.70   12.755%   $168.7942   $168.79   $168.80   $168.80  
  Purchase #5 $58.99   5.366%   $62.1554   $62.16   $62.15   $62.20  
  Purchase #6 $233.72   6.113%   $248.0073   $248.01   $248.00   $248.00  
  Purchase #7 $136.78   3.770%   $141.9366   $141.94   $141.95   $141.90  
  7 purchase totals = $1,122.67       $1,206.1954   $1,206.20   $1,206.20   $1,206.20