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 $207.79   6.328%   $220.939   $220.94   $220.95   $220.90  
  Purchase #2 $86.28   5.805%   $91.2886   $91.29   $91.30   $91.30  
  Purchase #3 $14.46   10.615%   $15.9949   $15.99   $16.00   $16.00  
  Purchase #4 $125.94   6.805%   $134.5102   $134.51   $134.50   $134.50  
  Purchase #5 $157.66   13.192%   $178.4585   $178.46   $178.45   $178.50  
  Purchase #6 $167.99   10.524%   $185.6693   $185.67   $185.65   $185.70  
  Purchase #7 $83.93   10.835%   $93.0238   $93.02   $93.00   $93.00  
  7 purchase totals = $844.05       $919.8843   $919.88   $919.85   $919.90