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 $69.66   11.440%   $77.6291   $77.63   $77.65   $77.60  
  Purchase #2 $26.91   7.643%   $28.9667   $28.97   $28.95   $29.00  
  Purchase #3 $59.46   9.180%   $64.9184   $64.92   $64.90   $64.90  
  Purchase #4 $248.29   3.741%   $257.5785   $257.58   $257.60   $257.60  
  Purchase #5 $134.76   9.339%   $147.3452   $147.35   $147.35   $147.30  
  Purchase #6 $167.46   9.719%   $183.7354   $183.74   $183.75   $183.70  
  Purchase #7 $39.49   11.205%   $43.9149   $43.91   $43.90   $43.90  
  7 purchase totals = $746.03       $804.0882   $804.10   $804.10   $804.00