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 $46.35   5.432%   $48.8677   $48.87   $48.85   $48.90  
  Purchase #2 $28.99   9.664%   $31.7916   $31.79   $31.80   $31.80  
  Purchase #3 $84.84   13.651%   $96.4215   $96.42   $96.40   $96.40  
  Purchase #4 $178.96   7.678%   $192.7005   $192.70   $192.70   $192.70  
  Purchase #5 $73.47   4.540%   $76.8055   $76.81   $76.80   $76.80  
  Purchase #6 $74.25   8.628%   $80.6563   $80.66   $80.65   $80.70  
  Purchase #7 $56.36   10.645%   $62.3595   $62.36   $62.35   $62.40  
  7 purchase totals = $543.22       $589.6026   $589.61   $589.55   $589.70