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 $114.45   5.606%   $120.8661   $120.87   $120.85   $120.90  
  Purchase #2 $131.29   13.569%   $149.1047   $149.10   $149.10   $149.10  
  Purchase #3 $203.71   7.162%   $218.2997   $218.30   $218.30   $218.30  
  Purchase #4 $181.99   8.573%   $197.592   $197.59   $197.60   $197.60  
  Purchase #5 $35.42   3.607%   $36.6976   $36.70   $36.70   $36.70  
  Purchase #6 $57.35   6.159%   $60.8822   $60.88   $60.90   $60.90  
  Purchase #7 $195.72   6.286%   $208.023   $208.02   $208.00   $208.00  
  7 purchase totals = $919.93       $991.4653   $991.46   $991.45   $991.50