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 $149.25   7.624%   $160.6288   $160.63   $160.65   $160.60  
  Purchase #2 $185.40   9.400%   $202.8276   $202.83   $202.85   $202.80  
  Purchase #3 $230.76   8.543%   $250.4738   $250.47   $250.45   $250.50  
  Purchase #4 $160.87   13.867%   $183.1778   $183.18   $183.20   $183.20  
  Purchase #5 $245.44   10.424%   $271.0247   $271.02   $271.00   $271.00  
  Purchase #6 $165.34   7.757%   $178.1654   $178.17   $178.15   $178.20  
  Purchase #7 $68.87   11.805%   $77.0001   $77.00   $77.00   $77.00  
  7 purchase totals = $1,205.93       $1,323.2982   $1,323.30   $1,323.30   $1,323.30