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 $61.34   3.736%   $63.6317   $63.63   $63.65   $63.60  
  Purchase #2 $12.39   13.232%   $14.0294   $14.03   $14.05   $14.00  
  Purchase #3 $243.66   7.407%   $261.7079   $261.71   $261.70   $261.70  
  Purchase #4 $163.47   12.121%   $183.2842   $183.28   $183.30   $183.30  
  Purchase #5 $49.42   8.141%   $53.4433   $53.44   $53.45   $53.40  
  Purchase #6 $23.47   9.397%   $25.6755   $25.68   $25.70   $25.70  
  Purchase #7 $95.94   5.799%   $101.5036   $101.50   $101.50   $101.50  
  7 purchase totals = $649.69       $703.2756   $703.27   $703.35   $703.20