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 $9.88   9.345%   $10.8033   $10.80   $10.80   $10.80  
  Purchase #2 $129.77   10.266%   $143.0922   $143.09   $143.10   $143.10  
  Purchase #3 $237.41   10.248%   $261.7398   $261.74   $261.75   $261.70  
  Purchase #4 $230.43   7.585%   $247.9081   $247.91   $247.90   $247.90  
  Purchase #5 $120.62   11.247%   $134.1861   $134.19   $134.20   $134.20  
  Purchase #6 $191.53   4.258%   $199.6853   $199.69   $199.70   $199.70  
  Purchase #7 $243.80   9.625%   $267.2658   $267.27   $267.25   $267.30  
  7 purchase totals = $1,163.44       $1,264.6806   $1,264.69   $1,264.70   $1,264.70