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 $86.63   12.624%   $97.5662   $97.57   $97.55   $97.60  
  Purchase #2 $118.82   10.859%   $131.7227   $131.72   $131.70   $131.70  
  Purchase #3 $51.59   11.698%   $57.625   $57.63   $57.65   $57.60  
  Purchase #4 $43.55   8.575%   $47.2844   $47.28   $47.30   $47.30  
  Purchase #5 $154.68   7.741%   $166.6538   $166.65   $166.65   $166.70  
  Purchase #6 $168.57   10.199%   $185.7625   $185.76   $185.75   $185.80  
  Purchase #7 $75.90   11.235%   $84.4274   $84.43   $84.45   $84.40  
  7 purchase totals = $699.74       $771.0420   $771.04   $771.05   $771.10