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 $50.33   12.459%   $56.6006   $56.60   $56.60   $56.60  
  Purchase #2 $68.36   7.256%   $73.3202   $73.32   $73.30   $73.30  
  Purchase #3 $116.28   3.681%   $120.5603   $120.56   $120.55   $120.60  
  Purchase #4 $31.58   9.602%   $34.6123   $34.61   $34.60   $34.60  
  Purchase #5 $200.77   12.217%   $225.2981   $225.30   $225.30   $225.30  
  Purchase #6 $86.89   7.693%   $93.5744   $93.57   $93.55   $93.60  
  Purchase #7 $128.54   11.209%   $142.948   $142.95   $142.95   $142.90  
  7 purchase totals = $682.75       $746.9139   $746.91   $746.85   $746.90