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 $192.99   9.656%   $211.6251   $211.63   $211.65   $211.60  
  Purchase #2 $42.48   10.325%   $46.8661   $46.87   $46.85   $46.90  
  Purchase #3 $10.77   3.774%   $11.1765   $11.18   $11.20   $11.20  
  Purchase #4 $70.82   4.794%   $74.2151   $74.22   $74.20   $74.20  
  Purchase #5 $179.71   12.824%   $202.756   $202.76   $202.75   $202.80  
  Purchase #6 $122.30   3.538%   $126.627   $126.63   $126.65   $126.60  
  Purchase #7 $67.56   3.855%   $70.1644   $70.16   $70.15   $70.20  
  7 purchase totals = $686.63       $743.4302   $743.45   $743.45   $743.50