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 $157.75   3.176%   $162.7601   $162.76   $162.75   $162.80  
  Purchase #2 $35.39   11.696%   $39.5292   $39.53   $39.55   $39.50  
  Purchase #3 $218.94   12.635%   $246.6031   $246.60   $246.60   $246.60  
  Purchase #4 $195.97   11.126%   $217.7736   $217.77   $217.75   $217.80  
  Purchase #5 $65.63   11.271%   $73.0272   $73.03   $73.05   $73.00  
  Purchase #6 $184.60   6.433%   $196.4753   $196.48   $196.50   $196.50  
  Purchase #7 $63.91   8.799%   $69.5334   $69.53   $69.55   $69.50  
  7 purchase totals = $922.19       $1,005.7019   $1,005.70   $1,005.75   $1,005.70