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 $43.97   13.651%   $49.9723   $49.97   $49.95   $50.00  
  Purchase #2 $81.44   7.869%   $87.8485   $87.85   $87.85   $87.80  
  Purchase #3 $90.96   7.633%   $97.903   $97.90   $97.90   $97.90  
  Purchase #4 $69.76   4.308%   $72.7653   $72.77   $72.75   $72.80  
  Purchase #5 $21.34   13.615%   $24.2454   $24.25   $24.25   $24.20  
  Purchase #6 $208.77   3.212%   $215.4757   $215.48   $215.50   $215.50  
  Purchase #7 $102.83   6.468%   $109.481   $109.48   $109.50   $109.50  
  7 purchase totals = $619.07       $657.6912   $657.70   $657.70   $657.70