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 $57.87   10.105%   $63.7178   $63.72   $63.70   $63.70  
  Purchase #2 $49.67   5.633%   $52.4679   $52.47   $52.45   $52.50  
  Purchase #3 $148.93   8.737%   $161.942   $161.94   $161.95   $161.90  
  Purchase #4 $198.29   5.113%   $208.4286   $208.43   $208.45   $208.40  
  Purchase #5 $234.36   5.693%   $247.7021   $247.70   $247.70   $247.70  
  Purchase #6 $30.82   3.719%   $31.9662   $31.97   $31.95   $32.00  
  Purchase #7 $240.81   10.533%   $266.1745   $266.17   $266.15   $266.20  
  7 purchase totals = $960.75       $1,032.3991   $1,032.40   $1,032.35   $1,032.40