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 $53.52   13.225%   $60.598   $60.60   $60.60   $60.60  
  Purchase #2 $14.54   11.258%   $16.1769   $16.18   $16.20   $16.20  
  Purchase #3 $61.52   13.579%   $69.8738   $69.87   $69.85   $69.90  
  Purchase #4 $44.29   6.813%   $47.3075   $47.31   $47.30   $47.30  
  Purchase #5 $183.25   4.158%   $190.8695   $190.87   $190.85   $190.90  
  Purchase #6 $137.45   3.851%   $142.7432   $142.74   $142.75   $142.70  
  Purchase #7 $68.75   4.128%   $71.588   $71.59   $71.60   $71.60  
  7 purchase totals = $563.32       $599.1569   $599.16   $599.15   $599.20