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 $56.73   11.758%   $63.4003   $63.40   $63.40   $63.40  
  Purchase #2 $162.25   8.626%   $176.2457   $176.25   $176.25   $176.20  
  Purchase #3 $85.65   11.798%   $95.755   $95.76   $95.75   $95.80  
  Purchase #4 $244.97   13.472%   $277.9724   $277.97   $277.95   $278.00  
  Purchase #5 $107.47   8.381%   $116.4771   $116.48   $116.50   $116.50  
  Purchase #6 $229.83   11.645%   $256.5937   $256.59   $256.60   $256.60  
  Purchase #7 $176.70   11.703%   $197.3792   $197.38   $197.40   $197.40  
  7 purchase totals = $1,063.60       $1,183.8234   $1,183.83   $1,183.85   $1,183.90