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 $154.78   4.462%   $161.6863   $161.69   $161.70   $161.70  
  Purchase #2 $33.80   5.850%   $35.7773   $35.78   $35.80   $35.80  
  Purchase #3 $119.53   4.542%   $124.9591   $124.96   $124.95   $125.00  
  Purchase #4 $240.94   11.634%   $268.971   $268.97   $268.95   $269.00  
  Purchase #5 $79.94   5.282%   $84.1624   $84.16   $84.15   $84.20  
  Purchase #6 $108.38   5.371%   $114.2011   $114.20   $114.20   $114.20  
  Purchase #7 $156.69   7.623%   $168.6345   $168.63   $168.65   $168.60  
  7 purchase totals = $894.06       $958.3917   $958.39   $958.40   $958.50