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 $236.79   4.843%   $248.2577   $248.26   $248.25   $248.30  
  Purchase #2 $95.97   10.295%   $105.8501   $105.85   $105.85   $105.90  
  Purchase #3 $234.92   4.688%   $245.933   $245.93   $245.95   $245.90  
  Purchase #4 $240.31   3.399%   $248.4781   $248.48   $248.50   $248.50  
  Purchase #5 $245.94   7.401%   $264.142   $264.14   $264.15   $264.10  
  Purchase #6 $142.67   7.740%   $153.7127   $153.71   $153.70   $153.70  
  Purchase #7 $159.96   5.300%   $168.4379   $168.44   $168.45   $168.40  
  7 purchase totals = $1,356.56       $1,434.8115   $1,434.81   $1,434.85   $1,434.80