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 $168.62   9.691%   $184.961   $184.96   $184.95   $185.00  
  Purchase #2 $186.79   3.401%   $193.1427   $193.14   $193.15   $193.10  
  Purchase #3 $149.39   3.313%   $154.3393   $154.34   $154.35   $154.30  
  Purchase #4 $179.42   6.857%   $191.7228   $191.72   $191.70   $191.70  
  Purchase #5 $212.92   4.834%   $223.2126   $223.21   $223.20   $223.20  
  Purchase #6 $221.99   13.636%   $252.2606   $252.26   $252.25   $252.30  
  Purchase #7 $61.81   7.397%   $66.3821   $66.38   $66.40   $66.40  
  7 purchase totals = $1,180.94       $1,266.0211   $1,266.01   $1,266.00   $1,266.00