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 $184.38   5.464%   $194.4545   $194.45   $194.45   $194.50  
  Purchase #2 $120.69   11.239%   $134.2543   $134.25   $134.25   $134.30  
  Purchase #3 $76.45   4.281%   $79.7228   $79.72   $79.70   $79.70  
  Purchase #4 $144.74   7.705%   $155.8922   $155.89   $155.90   $155.90  
  Purchase #5 $201.93   12.471%   $227.1127   $227.11   $227.10   $227.10  
  Purchase #6 $188.57   13.695%   $214.3947   $214.39   $214.40   $214.40  
  Purchase #7 $49.39   11.106%   $54.8753   $54.88   $54.90   $54.90  
  7 purchase totals = $966.15       $1,060.7065   $1,060.69   $1,060.70   $1,060.80