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 $114.53   10.562%   $126.6267   $126.63   $126.65   $126.60  
  Purchase #2 $61.79   9.620%   $67.7342   $67.73   $67.75   $67.70  
  Purchase #3 $46.74   9.129%   $51.0069   $51.01   $51.00   $51.00  
  Purchase #4 $145.77   7.706%   $157.003   $157.00   $157.00   $157.00  
  Purchase #5 $57.29   5.789%   $60.6065   $60.61   $60.60   $60.60  
  Purchase #6 $169.85   5.373%   $178.976   $178.98   $179.00   $179.00  
  Purchase #7 $135.75   11.806%   $151.7766   $151.78   $151.80   $151.80  
  7 purchase totals = $731.72       $793.7299   $793.74   $793.80   $793.70