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 $37.41   10.291%   $41.2599   $41.26   $41.25   $41.30  
  Purchase #2 $190.97   9.103%   $208.354   $208.35   $208.35   $208.40  
  Purchase #3 $154.38   6.763%   $164.8207   $164.82   $164.80   $164.80  
  Purchase #4 $232.64   9.226%   $254.1034   $254.10   $254.10   $254.10  
  Purchase #5 $246.81   4.785%   $258.6199   $258.62   $258.60   $258.60  
  Purchase #6 $244.52   3.625%   $253.3839   $253.38   $253.40   $253.40  
  Purchase #7 $17.64   10.175%   $19.4349   $19.43   $19.45   $19.40  
  7 purchase totals = $1,124.37       $1,199.9767   $1,199.96   $1,199.95   $1,200.00