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 $60.79   10.268%   $67.0319   $67.03   $67.05   $67.00  
  Purchase #2 $234.61   13.612%   $266.5451   $266.55   $266.55   $266.50  
  Purchase #3 $68.67   9.324%   $75.0728   $75.07   $75.05   $75.10  
  Purchase #4 $127.69   5.622%   $134.8687   $134.87   $134.85   $134.90  
  Purchase #5 $237.50   8.626%   $257.9868   $257.99   $258.00   $258.00  
  Purchase #6 $168.29   3.437%   $174.0741   $174.07   $174.05   $174.10  
  Purchase #7 $128.93   6.617%   $137.4613   $137.46   $137.45   $137.50  
  7 purchase totals = $1,026.48       $1,113.0407   $1,113.04   $1,113.00   $1,113.10