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 $61.53   3.301%   $63.5611   $63.56   $63.55   $63.60  
  Purchase #2 $125.68   11.668%   $140.3443   $140.34   $140.35   $140.30  
  Purchase #3 $14.37   4.465%   $15.0116   $15.01   $15.00   $15.00  
  Purchase #4 $162.67   9.854%   $178.6995   $178.70   $178.70   $178.70  
  Purchase #5 $21.30   5.478%   $22.4668   $22.47   $22.45   $22.50  
  Purchase #6 $69.73   13.380%   $79.0599   $79.06   $79.05   $79.10  
  Purchase #7 $31.34   8.115%   $33.8832   $33.88   $33.90   $33.90  
  7 purchase totals = $486.62       $533.0264   $533.02   $533.00   $533.10