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 $210.69   11.807%   $235.5662   $235.57   $235.55   $235.60  
  Purchase #2 $225.37   13.292%   $255.3262   $255.33   $255.35   $255.30  
  Purchase #3 $248.81   8.567%   $270.1256   $270.13   $270.15   $270.10  
  Purchase #4 $119.57   3.321%   $123.5409   $123.54   $123.55   $123.50  
  Purchase #5 $50.85   5.517%   $53.6554   $53.66   $53.65   $53.70  
  Purchase #6 $7.66   12.296%   $8.6019   $8.60   $8.60   $8.60  
  Purchase #7 $73.89   4.337%   $77.0946   $77.09   $77.10   $77.10  
  7 purchase totals = $936.84       $1,023.9108   $1,023.92   $1,023.95   $1,023.90