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 $58.61   12.688%   $66.0464   $66.05   $66.05   $66.00  
  Purchase #2 $229.68   11.118%   $255.2158   $255.22   $255.20   $255.20  
  Purchase #3 $103.36   10.532%   $114.2459   $114.25   $114.25   $114.20  
  Purchase #4 $247.56   5.770%   $261.8442   $261.84   $261.85   $261.80  
  Purchase #5 $161.86   9.350%   $176.9939   $176.99   $177.00   $177.00  
  Purchase #6 $165.66   4.437%   $173.0103   $173.01   $173.00   $173.00  
  Purchase #7 $214.94   9.461%   $235.2755   $235.28   $235.30   $235.30  
  7 purchase totals = $1,181.67       $1,282.6320   $1,282.64   $1,282.65   $1,282.50