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 $86.90   10.867%   $96.3434   $96.34   $96.35   $96.30  
  Purchase #2 $230.77   9.794%   $253.3716   $253.37   $253.35   $253.40  
  Purchase #3 $117.50   10.305%   $129.6084   $129.61   $129.60   $129.60  
  Purchase #4 $122.86   8.521%   $133.3289   $133.33   $133.35   $133.30  
  Purchase #5 $185.66   7.791%   $200.1248   $200.12   $200.10   $200.10  
  Purchase #6 $125.52   12.105%   $140.7142   $140.71   $140.70   $140.70  
  Purchase #7 $12.26   3.714%   $12.7153   $12.72   $12.70   $12.70  
  7 purchase totals = $881.47       $966.2066   $966.20   $966.15   $966.10