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 $24.90   10.810%   $27.5917   $27.59   $27.60   $27.60  
  Purchase #2 $221.57   6.803%   $236.6434   $236.64   $236.65   $236.60  
  Purchase #3 $240.69   3.472%   $249.0468   $249.05   $249.05   $249.00  
  Purchase #4 $24.70   7.286%   $26.4996   $26.50   $26.50   $26.50  
  Purchase #5 $245.31   9.789%   $269.3234   $269.32   $269.30   $269.30  
  Purchase #6 $127.32   4.497%   $133.0456   $133.05   $133.05   $133.00  
  Purchase #7 $74.68   7.803%   $80.5073   $80.51   $80.50   $80.50  
  7 purchase totals = $959.17       $1,022.6578   $1,022.66   $1,022.65   $1,022.50