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 $248.75   4.848%   $260.8094   $260.81   $260.80   $260.80  
  Purchase #2 $57.62   5.148%   $60.5863   $60.59   $60.60   $60.60  
  Purchase #3 $24.53   8.395%   $26.5893   $26.59   $26.60   $26.60  
  Purchase #4 $50.27   5.243%   $52.9057   $52.91   $52.90   $52.90  
  Purchase #5 $96.74   4.605%   $101.1949   $101.19   $101.20   $101.20  
  Purchase #6 $166.57   8.165%   $180.1704   $180.17   $180.15   $180.20  
  Purchase #7 $238.40   3.712%   $247.2494   $247.25   $247.25   $247.20  
  7 purchase totals = $882.88       $929.5054   $929.51   $929.50   $929.50