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 $208.95   8.468%   $226.6439   $226.64   $226.65   $226.60  
  Purchase #2 $86.35   9.189%   $94.2847   $94.28   $94.30   $94.30  
  Purchase #3 $180.44   6.804%   $192.7171   $192.72   $192.70   $192.70  
  Purchase #4 $68.37   7.746%   $73.6659   $73.67   $73.65   $73.70  
  Purchase #5 $172.54   4.604%   $180.4837   $180.48   $180.50   $180.50  
  Purchase #6 $127.81   7.660%   $137.6002   $137.60   $137.60   $137.60  
  Purchase #7 $116.39   12.103%   $130.4767   $130.48   $130.50   $130.50  
  7 purchase totals = $960.85       $1,035.8722   $1,035.87   $1,035.90   $1,035.90