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 $241.60   11.502%   $269.3888   $269.39   $269.40   $269.40  
  Purchase #2 $73.98   3.687%   $76.7076   $76.71   $76.70   $76.70  
  Purchase #3 $91.35   9.417%   $99.9524   $99.95   $99.95   $100.00  
  Purchase #4 $54.59   5.538%   $57.6132   $57.61   $57.60   $57.60  
  Purchase #5 $13.29   5.335%   $13.999   $14.00   $14.00   $14.00  
  Purchase #6 $211.76   3.632%   $219.4511   $219.45   $219.45   $219.50  
  Purchase #7 $207.36   11.611%   $231.4366   $231.44   $231.45   $231.40  
  7 purchase totals = $893.93       $968.5487   $968.55   $968.55   $968.60