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 $141.80   8.274%   $153.5325   $153.53   $153.55   $153.50  
  Purchase #2 $239.39   13.809%   $272.4474   $272.45   $272.45   $272.40  
  Purchase #3 $24.97   6.350%   $26.5556   $26.56   $26.55   $26.60  
  Purchase #4 $153.81   6.265%   $163.4462   $163.45   $163.45   $163.40  
  Purchase #5 $63.46   11.544%   $70.7858   $70.79   $70.80   $70.80  
  Purchase #6 $180.42   3.345%   $186.455   $186.46   $186.45   $186.50  
  Purchase #7 $228.62   9.558%   $250.4715   $250.47   $250.45   $250.50  
  7 purchase totals = $1,032.47       $1,123.6940   $1,123.71   $1,123.70   $1,123.70