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 $95.62   8.286%   $103.5431   $103.54   $103.55   $103.50  
  Purchase #2 $201.61   4.822%   $211.3316   $211.33   $211.35   $211.30  
  Purchase #3 $30.36   8.287%   $32.8759   $32.88   $32.90   $32.90  
  Purchase #4 $198.60   4.816%   $208.1646   $208.16   $208.15   $208.20  
  Purchase #5 $212.87   12.141%   $238.7145   $238.71   $238.70   $238.70  
  Purchase #6 $111.91   4.609%   $117.0679   $117.07   $117.05   $117.10  
  Purchase #7 $118.97   12.377%   $133.6949   $133.69   $133.70   $133.70  
  7 purchase totals = $969.94       $1,045.3925   $1,045.38   $1,045.40   $1,045.40