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 $79.87   10.480%   $88.2404   $88.24   $88.25   $88.20  
  Purchase #2 $202.34   11.712%   $226.0381   $226.04   $226.05   $226.00  
  Purchase #3 $94.74   11.149%   $105.3026   $105.30   $105.30   $105.30  
  Purchase #4 $69.97   9.520%   $76.6311   $76.63   $76.65   $76.60  
  Purchase #5 $61.84   5.341%   $65.1429   $65.14   $65.15   $65.10  
  Purchase #6 $125.76   9.624%   $137.8631   $137.86   $137.85   $137.90  
  Purchase #7 $44.60   4.436%   $46.5785   $46.58   $46.60   $46.60  
  7 purchase totals = $679.12       $745.7967   $745.79   $745.85   $745.70