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 $110.49   7.106%   $118.3414   $118.34   $118.35   $118.30  
  Purchase #2 $231.50   13.415%   $262.5557   $262.56   $262.55   $262.60  
  Purchase #3 $101.68   13.259%   $115.1618   $115.16   $115.15   $115.20  
  Purchase #4 $101.92   7.563%   $109.6282   $109.63   $109.65   $109.60  
  Purchase #5 $32.64   10.246%   $35.9843   $35.98   $36.00   $36.00  
  Purchase #6 $114.26   11.284%   $127.1531   $127.15   $127.15   $127.20  
  Purchase #7 $6.95   7.298%   $7.4572   $7.46   $7.45   $7.50  
  7 purchase totals = $699.44       $776.2817   $776.28   $776.30   $776.40