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 $151.90   8.119%   $164.2328   $164.23   $164.25   $164.20  
  Purchase #2 $187.90   9.480%   $205.7129   $205.71   $205.70   $205.70  
  Purchase #3 $20.96   13.377%   $23.7638   $23.76   $23.75   $23.80  
  Purchase #4 $175.54   4.403%   $183.269   $183.27   $183.25   $183.30  
  Purchase #5 $222.67   6.481%   $237.1012   $237.10   $237.10   $237.10  
  Purchase #6 $52.51   9.772%   $57.6413   $57.64   $57.65   $57.60  
  Purchase #7 $124.92   3.180%   $128.8925   $128.89   $128.90   $128.90  
  7 purchase totals = $936.40       $1,000.6135   $1,000.60   $1,000.60   $1,000.60