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 $32.77   5.157%   $34.4599   $34.46   $34.45   $34.50  
  Purchase #2 $130.93   4.496%   $136.8166   $136.82   $136.80   $136.80  
  Purchase #3 $45.92   7.866%   $49.5321   $49.53   $49.55   $49.50  
  Purchase #4 $213.99   13.423%   $242.7139   $242.71   $242.70   $242.70  
  Purchase #5 $164.65   12.359%   $184.9991   $185.00   $185.00   $185.00  
  Purchase #6 $221.33   6.489%   $235.6921   $235.69   $235.70   $235.70  
  Purchase #7 $73.33   3.343%   $75.7814   $75.78   $75.80   $75.80  
  7 purchase totals = $882.92       $959.9951   $959.99   $960.00   $960.00