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 $175.78   12.123%   $197.0898   $197.09   $197.10   $197.10  
  Purchase #2 $209.42   5.188%   $220.2847   $220.28   $220.30   $220.30  
  Purchase #3 $35.56   11.522%   $39.6572   $39.66   $39.65   $39.70  
  Purchase #4 $155.73   13.440%   $176.6601   $176.66   $176.65   $176.70  
  Purchase #5 $51.70   3.645%   $53.5845   $53.58   $53.60   $53.60  
  Purchase #6 $194.35   3.501%   $201.1542   $201.15   $201.15   $201.20  
  Purchase #7 $96.49   10.512%   $106.633   $106.63   $106.65   $106.60  
  7 purchase totals = $919.03       $995.0635   $995.05   $995.10   $995.20