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 $85.62   12.540%   $96.3567   $96.36   $96.35   $96.40  
  Purchase #2 $173.96   5.556%   $183.6252   $183.63   $183.65   $183.60  
  Purchase #3 $68.55   5.444%   $72.2819   $72.28   $72.30   $72.30  
  Purchase #4 $218.27   3.667%   $226.274   $226.27   $226.25   $226.30  
  Purchase #5 $92.69   9.860%   $101.8292   $101.83   $101.85   $101.80  
  Purchase #6 $55.60   5.315%   $58.5551   $58.56   $58.55   $58.60  
  Purchase #7 $109.81   8.421%   $119.0571   $119.06   $119.05   $119.10  
  7 purchase totals = $804.50       $857.9792   $857.99   $858.00   $858.10