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 $57.46   10.170%   $63.3037   $63.30   $63.30   $63.30  
  Purchase #2 $95.89   9.190%   $104.7023   $104.70   $104.70   $104.70  
  Purchase #3 $61.78   6.369%   $65.7148   $65.71   $65.70   $65.70  
  Purchase #4 $185.94   3.685%   $192.7919   $192.79   $192.80   $192.80  
  Purchase #5 $126.63   13.205%   $143.3515   $143.35   $143.35   $143.40  
  Purchase #6 $106.78   9.605%   $117.0362   $117.04   $117.05   $117.00  
  Purchase #7 $15.47   12.569%   $17.4144   $17.41   $17.40   $17.40  
  7 purchase totals = $649.95       $704.3148   $704.30   $704.30   $704.30