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 $150.61   3.138%   $155.3361   $155.34   $155.35   $155.30  
  Purchase #2 $201.79   3.375%   $208.6004   $208.60   $208.60   $208.60  
  Purchase #3 $168.60   8.862%   $183.5413   $183.54   $183.55   $183.50  
  Purchase #4 $95.40   11.545%   $106.4139   $106.41   $106.40   $106.40  
  Purchase #5 $53.49   9.497%   $58.5699   $58.57   $58.55   $58.60  
  Purchase #6 $65.37   5.207%   $68.7738   $68.77   $68.75   $68.80  
  Purchase #7 $214.51   5.452%   $226.2051   $226.21   $226.20   $226.20  
  7 purchase totals = $949.77       $1,007.4405   $1,007.44   $1,007.40   $1,007.40