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 $57.56   13.486%   $65.3225   $65.32   $65.30   $65.30  
  Purchase #2 $239.64   9.365%   $262.0823   $262.08   $262.10   $262.10  
  Purchase #3 $188.82   9.226%   $206.2405   $206.24   $206.25   $206.20  
  Purchase #4 $214.86   4.747%   $225.0594   $225.06   $225.05   $225.10  
  Purchase #5 $94.97   10.715%   $105.146   $105.15   $105.15   $105.10  
  Purchase #6 $134.74   12.211%   $151.1931   $151.19   $151.20   $151.20  
  Purchase #7 $99.50   8.186%   $107.6451   $107.65   $107.65   $107.60  
  7 purchase totals = $1,030.09       $1,122.6889   $1,122.69   $1,122.70   $1,122.60