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 $60.43   5.750%   $63.9047   $63.90   $63.90   $63.90  
  Purchase #2 $49.74   9.379%   $54.4051   $54.41   $54.40   $54.40  
  Purchase #3 $167.69   11.318%   $186.6692   $186.67   $186.65   $186.70  
  Purchase #4 $12.99   13.316%   $14.7197   $14.72   $14.70   $14.70  
  Purchase #5 $224.80   12.274%   $252.392   $252.39   $252.40   $252.40  
  Purchase #6 $196.66   6.157%   $208.7684   $208.77   $208.75   $208.80  
  Purchase #7 $20.70   6.740%   $22.0952   $22.10   $22.10   $22.10  
  7 purchase totals = $733.01       $802.9543   $802.96   $802.90   $803.00