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 $202.92   12.260%   $227.798   $227.80   $227.80   $227.80  
  Purchase #2 $102.43   11.222%   $113.9247   $113.92   $113.90   $113.90  
  Purchase #3 $248.92   7.491%   $267.5666   $267.57   $267.55   $267.60  
  Purchase #4 $74.81   7.584%   $80.4836   $80.48   $80.50   $80.50  
  Purchase #5 $197.54   13.697%   $224.5971   $224.60   $224.60   $224.60  
  Purchase #6 $119.70   3.431%   $123.8069   $123.81   $123.80   $123.80  
  Purchase #7 $244.79   5.622%   $258.5521   $258.55   $258.55   $258.60  
  7 purchase totals = $1,191.11       $1,296.7290   $1,296.73   $1,296.70   $1,296.80