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 $90.72   8.263%   $98.2162   $98.22   $98.20   $98.20  
  Purchase #2 $96.34   3.679%   $99.8843   $99.88   $99.90   $99.90  
  Purchase #3 $139.30   9.542%   $152.592   $152.59   $152.60   $152.60  
  Purchase #4 $49.41   5.330%   $52.0436   $52.04   $52.05   $52.00  
  Purchase #5 $190.51   4.341%   $198.78   $198.78   $198.80   $198.80  
  Purchase #6 $224.48   13.407%   $254.576   $254.58   $254.60   $254.60  
  Purchase #7 $14.99   13.509%   $17.015   $17.02   $17.00   $17.00  
  7 purchase totals = $805.75       $873.1071   $873.11   $873.15   $873.10