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 $242.37   8.430%   $262.8018   $262.80   $262.80   $262.80  
  Purchase #2 $54.56   3.108%   $56.2557   $56.26   $56.25   $56.30  
  Purchase #3 $226.54   7.763%   $244.1263   $244.13   $244.15   $244.10  
  Purchase #4 $48.91   8.503%   $53.0688   $53.07   $53.05   $53.10  
  Purchase #5 $158.56   12.801%   $178.8573   $178.86   $178.85   $178.90  
  Purchase #6 $57.62   13.484%   $65.3895   $65.39   $65.40   $65.40  
  Purchase #7 $196.58   3.233%   $202.9354   $202.94   $202.95   $202.90  
  7 purchase totals = $985.14       $1,063.4348   $1,063.45   $1,063.45   $1,063.50