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 $73.64   5.454%   $77.6563   $77.66   $77.65   $77.70  
  Purchase #2 $49.85   3.315%   $51.5025   $51.50   $51.50   $51.50  
  Purchase #3 $120.42   4.361%   $125.6715   $125.67   $125.65   $125.70  
  Purchase #4 $183.93   11.507%   $205.0948   $205.09   $205.10   $205.10  
  Purchase #5 $124.91   12.236%   $140.194   $140.19   $140.20   $140.20  
  Purchase #6 $168.84   12.240%   $189.506   $189.51   $189.50   $189.50  
  Purchase #7 $72.83   4.388%   $76.0258   $76.03   $76.05   $76.00  
  7 purchase totals = $794.42       $865.6509   $865.65   $865.65   $865.70