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 $184.93   4.307%   $192.8949   $192.89   $192.90   $192.90  
  Purchase #2 $246.88   10.442%   $272.6592   $272.66   $272.65   $272.70  
  Purchase #3 $163.93   5.581%   $173.0789   $173.08   $173.10   $173.10  
  Purchase #4 $58.72   8.524%   $63.7253   $63.73   $63.75   $63.70  
  Purchase #5 $151.25   3.442%   $156.456   $156.46   $156.45   $156.50  
  Purchase #6 $179.49   7.731%   $193.3664   $193.37   $193.35   $193.40  
  Purchase #7 $56.41   3.209%   $58.2202   $58.22   $58.20   $58.20  
  7 purchase totals = $1,041.61       $1,110.4009   $1,110.41   $1,110.40   $1,110.50