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 $238.41   10.159%   $262.6301   $262.63   $262.65   $262.60  
  Purchase #2 $173.63   6.429%   $184.7927   $184.79   $184.80   $184.80  
  Purchase #3 $104.25   8.137%   $112.7328   $112.73   $112.75   $112.70  
  Purchase #4 $200.37   7.320%   $215.0371   $215.04   $215.05   $215.00  
  Purchase #5 $13.54   4.809%   $14.1911   $14.19   $14.20   $14.20  
  Purchase #6 $101.92   12.155%   $114.3084   $114.31   $114.30   $114.30  
  Purchase #7 $86.40   4.600%   $90.3744   $90.37   $90.35   $90.40  
  7 purchase totals = $918.52       $994.0666   $994.06   $994.10   $994.00