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 $9.28   4.180%   $9.6679   $9.67   $9.65   $9.70  
  Purchase #2 $44.92   8.168%   $48.5891   $48.59   $48.60   $48.60  
  Purchase #3 $176.33   4.102%   $183.5631   $183.56   $183.55   $183.60  
  Purchase #4 $88.69   12.568%   $99.8366   $99.84   $99.85   $99.80  
  Purchase #5 $248.68   4.517%   $259.9129   $259.91   $259.90   $259.90  
  Purchase #6 $196.50   9.759%   $215.6764   $215.68   $215.70   $215.70  
  Purchase #7 $156.34   3.448%   $161.7306   $161.73   $161.75   $161.70  
  7 purchase totals = $920.74       $978.9766   $978.98   $979.00   $979.00