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 $44.35   9.548%   $48.5845   $48.58   $48.60   $48.60  
  Purchase #2 $240.59   7.389%   $258.3672   $258.37   $258.35   $258.40  
  Purchase #3 $124.75   8.267%   $135.0631   $135.06   $135.05   $135.10  
  Purchase #4 $184.55   3.805%   $191.5721   $191.57   $191.55   $191.60  
  Purchase #5 $119.33   4.325%   $124.491   $124.49   $124.50   $124.50  
  Purchase #6 $67.30   4.503%   $70.3305   $70.33   $70.35   $70.30  
  Purchase #7 $47.77   4.487%   $49.9134   $49.91   $49.90   $49.90  
  7 purchase totals = $828.64       $878.3218   $878.31   $878.30   $878.40