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 $43.87   13.248%   $49.6819   $49.68   $49.70   $49.70  
  Purchase #2 $151.63   8.168%   $164.0151   $164.02   $164.00   $164.00  
  Purchase #3 $239.59   11.734%   $267.7035   $267.70   $267.70   $267.70  
  Purchase #4 $177.56   6.125%   $188.4356   $188.44   $188.45   $188.40  
  Purchase #5 $115.59   10.169%   $127.3443   $127.34   $127.35   $127.30  
  Purchase #6 $51.40   9.570%   $56.319   $56.32   $56.30   $56.30  
  Purchase #7 $234.58   6.284%   $249.321   $249.32   $249.30   $249.30  
  7 purchase totals = $1,014.22       $1,102.8204   $1,102.82   $1,102.80   $1,102.70