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 $86.29   11.821%   $96.4903   $96.49   $96.50   $96.50  
  Purchase #2 $134.31   10.780%   $148.7886   $148.79   $148.80   $148.80  
  Purchase #3 $238.82   11.232%   $265.6443   $265.64   $265.65   $265.60  
  Purchase #4 $30.71   13.698%   $34.9167   $34.92   $34.90   $34.90  
  Purchase #5 $167.55   12.404%   $188.3329   $188.33   $188.35   $188.30  
  Purchase #6 $207.71   8.297%   $224.9437   $224.94   $224.95   $224.90  
  Purchase #7 $193.77   7.584%   $208.4655   $208.47   $208.45   $208.50  
  7 purchase totals = $1,059.16       $1,167.5820   $1,167.58   $1,167.60   $1,167.50