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 $190.61   8.570%   $206.9453   $206.95   $206.95   $206.90  
  Purchase #2 $126.36   8.579%   $137.2004   $137.20   $137.20   $137.20  
  Purchase #3 $20.95   3.379%   $21.6579   $21.66   $21.65   $21.70  
  Purchase #4 $182.66   4.740%   $191.3181   $191.32   $191.30   $191.30  
  Purchase #5 $208.34   10.841%   $230.9261   $230.93   $230.95   $230.90  
  Purchase #6 $161.66   12.275%   $181.5038   $181.50   $181.50   $181.50  
  Purchase #7 $14.98   11.137%   $16.6483   $16.65   $16.65   $16.60  
  7 purchase totals = $905.56       $986.1999   $986.21   $986.20   $986.10