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 $94.82   11.335%   $105.5678   $105.57   $105.55   $105.60  
  Purchase #2 $156.54   7.648%   $168.5122   $168.51   $168.50   $168.50  
  Purchase #3 $75.66   10.451%   $83.5672   $83.57   $83.55   $83.60  
  Purchase #4 $150.75   13.459%   $171.0394   $171.04   $171.05   $171.00  
  Purchase #5 $225.49   7.405%   $242.1875   $242.19   $242.20   $242.20  
  Purchase #6 $201.75   3.198%   $208.202   $208.20   $208.20   $208.20  
  Purchase #7 $186.26   10.462%   $205.7465   $205.75   $205.75   $205.70  
  7 purchase totals = $1,091.27       $1,184.8226   $1,184.83   $1,184.80   $1,184.80