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 $106.73   9.216%   $116.5662   $116.57   $116.55   $116.60  
  Purchase #2 $248.27   8.372%   $269.0552   $269.06   $269.05   $269.10  
  Purchase #3 $109.49   5.209%   $115.1933   $115.19   $115.20   $115.20  
  Purchase #4 $197.94   5.533%   $208.892   $208.89   $208.90   $208.90  
  Purchase #5 $62.49   12.200%   $70.1138   $70.11   $70.10   $70.10  
  Purchase #6 $214.62   11.332%   $238.9407   $238.94   $238.95   $238.90  
  Purchase #7 $42.49   8.252%   $45.9963   $46.00   $46.00   $46.00  
  7 purchase totals = $982.03       $1,064.7575   $1,064.76   $1,064.75   $1,064.80