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 $156.59   5.118%   $164.6043   $164.60   $164.60   $164.60  
  Purchase #2 $239.49   11.336%   $266.6386   $266.64   $266.65   $266.60  
  Purchase #3 $37.31   3.616%   $38.6591   $38.66   $38.65   $38.70  
  Purchase #4 $175.39   5.640%   $185.282   $185.28   $185.30   $185.30  
  Purchase #5 $96.64   11.119%   $107.3854   $107.39   $107.40   $107.40  
  Purchase #6 $168.31   8.369%   $182.3959   $182.40   $182.40   $182.40  
  Purchase #7 $234.96   6.801%   $250.9396   $250.94   $250.95   $250.90  
  7 purchase totals = $1,108.69       $1,195.9049   $1,195.91   $1,195.95   $1,195.90