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 $243.94   10.643%   $269.9025   $269.90   $269.90   $269.90  
  Purchase #2 $35.29   8.796%   $38.3941   $38.39   $38.40   $38.40  
  Purchase #3 $11.64   9.639%   $12.762   $12.76   $12.75   $12.80  
  Purchase #4 $214.72   11.359%   $239.11   $239.11   $239.10   $239.10  
  Purchase #5 $189.82   10.490%   $209.7321   $209.73   $209.75   $209.70  
  Purchase #6 $196.99   5.351%   $207.5309   $207.53   $207.55   $207.50  
  Purchase #7 $151.47   11.308%   $168.5982   $168.60   $168.60   $168.60  
  7 purchase totals = $1,043.87       $1,146.0298   $1,146.02   $1,146.05   $1,146.00