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 $45.47   6.381%   $48.3714   $48.37   $48.35   $48.40  
  Purchase #2 $195.93   6.351%   $208.3735   $208.37   $208.35   $208.40  
  Purchase #3 $200.80   12.586%   $226.0727   $226.07   $226.05   $226.10  
  Purchase #4 $116.95   6.262%   $124.2734   $124.27   $124.25   $124.30  
  Purchase #5 $244.40   7.163%   $261.9064   $261.91   $261.90   $261.90  
  Purchase #6 $99.34   7.174%   $106.4667   $106.47   $106.45   $106.50  
  Purchase #7 $118.72   3.491%   $122.8645   $122.86   $122.85   $122.90  
  7 purchase totals = $1,021.61       $1,098.3286   $1,098.32   $1,098.20   $1,098.50