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 $57.82   11.836%   $64.6636   $64.66   $64.65   $64.70  
  Purchase #2 $63.84   3.697%   $66.2002   $66.20   $66.20   $66.20  
  Purchase #3 $131.71   11.676%   $147.0885   $147.09   $147.10   $147.10  
  Purchase #4 $51.90   8.647%   $56.3878   $56.39   $56.40   $56.40  
  Purchase #5 $182.51   12.702%   $205.6924   $205.69   $205.70   $205.70  
  Purchase #6 $80.80   11.741%   $90.2867   $90.29   $90.30   $90.30  
  Purchase #7 $241.98   10.394%   $267.1314   $267.13   $267.15   $267.10  
  7 purchase totals = $810.56       $897.4506   $897.45   $897.50   $897.50