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 $206.67   13.560%   $234.6945   $234.69   $234.70   $234.70  
  Purchase #2 $233.59   5.248%   $245.8488   $245.85   $245.85   $245.80  
  Purchase #3 $245.37   8.597%   $266.4645   $266.46   $266.45   $266.50  
  Purchase #4 $88.33   5.437%   $93.1325   $93.13   $93.15   $93.10  
  Purchase #5 $232.76   11.344%   $259.1643   $259.16   $259.15   $259.20  
  Purchase #6 $204.71   3.274%   $211.4122   $211.41   $211.40   $211.40  
  Purchase #7 $101.48   12.430%   $114.094   $114.09   $114.10   $114.10  
  7 purchase totals = $1,312.91       $1,424.8108   $1,424.79   $1,424.80   $1,424.80