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 $93.93   7.561%   $101.032   $101.03   $101.05   $101.00  
  Purchase #2 $23.43   12.646%   $26.393   $26.39   $26.40   $26.40  
  Purchase #3 $163.41   7.154%   $175.1004   $175.10   $175.10   $175.10  
  Purchase #4 $32.94   4.368%   $34.3788   $34.38   $34.40   $34.40  
  Purchase #5 $196.25   5.317%   $206.6846   $206.68   $206.70   $206.70  
  Purchase #6 $29.55   3.293%   $30.5231   $30.52   $30.50   $30.50  
  Purchase #7 $94.62   8.422%   $102.5889   $102.59   $102.60   $102.60  
  7 purchase totals = $634.13       $676.7008   $676.69   $676.75   $676.70