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 $239.62   10.123%   $263.8767   $263.88   $263.90   $263.90  
  Purchase #2 $201.84   4.809%   $211.5465   $211.55   $211.55   $211.50  
  Purchase #3 $30.90   7.376%   $33.1792   $33.18   $33.20   $33.20  
  Purchase #4 $76.32   13.249%   $86.4316   $86.43   $86.45   $86.40  
  Purchase #5 $43.76   7.382%   $46.9904   $46.99   $47.00   $47.00  
  Purchase #6 $193.47   11.308%   $215.3476   $215.35   $215.35   $215.30  
  Purchase #7 $92.42   13.130%   $104.5547   $104.55   $104.55   $104.60  
  7 purchase totals = $878.33       $961.9267   $961.93   $962.00   $961.90