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 $70.41   8.728%   $76.5554   $76.56   $76.55   $76.60  
  Purchase #2 $186.44   4.217%   $194.3022   $194.30   $194.30   $194.30  
  Purchase #3 $191.87   8.229%   $207.659   $207.66   $207.65   $207.70  
  Purchase #4 $228.84   3.507%   $236.8654   $236.87   $236.85   $236.90  
  Purchase #5 $45.76   8.824%   $49.7979   $49.80   $49.80   $49.80  
  Purchase #6 $82.99   12.675%   $93.509   $93.51   $93.50   $93.50  
  Purchase #7 $133.83   5.810%   $141.6055   $141.61   $141.60   $141.60  
  7 purchase totals = $940.14       $1,000.2944   $1,000.31   $1,000.25   $1,000.40