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 $101.87   4.132%   $106.0793   $106.08   $106.10   $106.10  
  Purchase #2 $232.94   12.152%   $261.2469   $261.25   $261.25   $261.20  
  Purchase #3 $33.40   5.481%   $35.2307   $35.23   $35.25   $35.20  
  Purchase #4 $12.61   13.338%   $14.2919   $14.29   $14.30   $14.30  
  Purchase #5 $151.79   5.660%   $160.3813   $160.38   $160.40   $160.40  
  Purchase #6 $239.92   5.830%   $253.9073   $253.91   $253.90   $253.90  
  Purchase #7 $224.57   8.368%   $243.362   $243.36   $243.35   $243.40  
  7 purchase totals = $997.10       $1,074.4994   $1,074.50   $1,074.55   $1,074.50