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 $193.49   11.654%   $216.0393   $216.04   $216.05   $216.00  
  Purchase #2 $13.47   7.718%   $14.5096   $14.51   $14.50   $14.50  
  Purchase #3 $115.86   6.559%   $123.4593   $123.46   $123.45   $123.50  
  Purchase #4 $34.45   9.351%   $37.6714   $37.67   $37.65   $37.70  
  Purchase #5 $86.86   5.371%   $91.5253   $91.53   $91.55   $91.50  
  Purchase #6 $124.67   8.503%   $135.2707   $135.27   $135.25   $135.30  
  Purchase #7 $129.89   3.232%   $134.088   $134.09   $134.10   $134.10  
  7 purchase totals = $698.69       $752.5636   $752.57   $752.55   $752.60