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 $64.82   12.796%   $73.1144   $73.11   $73.10   $73.10  
  Purchase #2 $101.68   13.701%   $115.6112   $115.61   $115.60   $115.60  
  Purchase #3 $13.66   5.648%   $14.4315   $14.43   $14.45   $14.40  
  Purchase #4 $147.73   10.427%   $163.1338   $163.13   $163.15   $163.10  
  Purchase #5 $60.88   13.683%   $69.2102   $69.21   $69.20   $69.20  
  Purchase #6 $67.89   11.260%   $75.5344   $75.53   $75.55   $75.50  
  Purchase #7 $214.36   9.229%   $234.1433   $234.14   $234.15   $234.10  
  7 purchase totals = $671.02       $745.1788   $745.16   $745.20   $745.00