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 $235.91   11.464%   $262.9547   $262.95   $262.95   $263.00  
  Purchase #2 $68.84   8.457%   $74.6618   $74.66   $74.65   $74.70  
  Purchase #3 $157.45   11.200%   $175.0844   $175.08   $175.10   $175.10  
  Purchase #4 $76.89   5.127%   $80.8322   $80.83   $80.85   $80.80  
  Purchase #5 $145.76   7.764%   $157.0768   $157.08   $157.10   $157.10  
  Purchase #6 $247.41   5.632%   $261.3441   $261.34   $261.35   $261.30  
  Purchase #7 $226.87   6.470%   $241.5485   $241.55   $241.55   $241.50  
  7 purchase totals = $1,159.13       $1,253.5025   $1,253.49   $1,253.55   $1,253.50