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 $248.43   5.164%   $261.2589   $261.26   $261.25   $261.30  
  Purchase #2 $215.64   10.475%   $238.2283   $238.23   $238.25   $238.20  
  Purchase #3 $86.99   10.375%   $96.0152   $96.02   $96.00   $96.00  
  Purchase #4 $9.82   5.793%   $10.3889   $10.39   $10.40   $10.40  
  Purchase #5 $163.69   7.309%   $175.6541   $175.65   $175.65   $175.70  
  Purchase #6 $98.82   8.642%   $107.36   $107.36   $107.35   $107.40  
  Purchase #7 $27.94   5.797%   $29.5597   $29.56   $29.55   $29.60  
  7 purchase totals = $851.33       $918.4651   $918.47   $918.45   $918.60