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 $57.63   10.148%   $63.4783   $63.48   $63.50   $63.50  
  Purchase #2 $69.30   9.585%   $75.9424   $75.94   $75.95   $75.90  
  Purchase #3 $32.31   7.745%   $34.8124   $34.81   $34.80   $34.80  
  Purchase #4 $166.96   9.466%   $182.7644   $182.76   $182.75   $182.80  
  Purchase #5 $240.93   12.191%   $270.3018   $270.30   $270.30   $270.30  
  Purchase #6 $222.73   12.246%   $250.0055   $250.01   $250.00   $250.00  
  Purchase #7 $130.56   10.616%   $144.4202   $144.42   $144.40   $144.40  
  7 purchase totals = $920.42       $1,021.7250   $1,021.72   $1,021.70   $1,021.70