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 $230.94   8.502%   $250.5745   $250.57   $250.55   $250.60  
  Purchase #2 $68.61   11.249%   $76.3279   $76.33   $76.35   $76.30  
  Purchase #3 $119.46   3.834%   $124.0401   $124.04   $124.05   $124.00  
  Purchase #4 $106.63   11.796%   $119.2081   $119.21   $119.20   $119.20  
  Purchase #5 $175.80   6.277%   $186.835   $186.84   $186.85   $186.80  
  Purchase #6 $113.32   3.128%   $116.8646   $116.86   $116.85   $116.90  
  Purchase #7 $144.70   5.500%   $152.6585   $152.66   $152.65   $152.70  
  7 purchase totals = $959.46       $1,026.5087   $1,026.51   $1,026.50   $1,026.50