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 $44.26   11.564%   $49.3782   $49.38   $49.40   $49.40  
  Purchase #2 $107.70   9.868%   $118.3278   $118.33   $118.35   $118.30  
  Purchase #3 $82.68   4.678%   $86.5478   $86.55   $86.55   $86.50  
  Purchase #4 $250.78   4.519%   $262.1127   $262.11   $262.10   $262.10  
  Purchase #5 $244.46   5.718%   $258.4382   $258.44   $258.45   $258.40  
  Purchase #6 $164.86   4.387%   $172.0924   $172.09   $172.10   $172.10  
  Purchase #7 $74.54   8.564%   $80.9236   $80.92   $80.90   $80.90  
  7 purchase totals = $969.28       $1,027.8207   $1,027.82   $1,027.85   $1,027.70