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 $92.68   6.353%   $98.568   $98.57   $98.55   $98.60  
  Purchase #2 $231.35   9.423%   $253.1501   $253.15   $253.15   $253.20  
  Purchase #3 $115.37   9.338%   $126.1433   $126.14   $126.15   $126.10  
  Purchase #4 $202.48   4.517%   $211.626   $211.63   $211.65   $211.60  
  Purchase #5 $21.84   11.848%   $24.4276   $24.43   $24.45   $24.40  
  Purchase #6 $6.55   6.739%   $6.9914   $6.99   $7.00   $7.00  
  Purchase #7 $142.29   9.391%   $155.6525   $155.65   $155.65   $155.70  
  7 purchase totals = $812.56       $876.5589   $876.56   $876.60   $876.60