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 $69.98   9.513%   $76.6372   $76.64   $76.65   $76.60  
  Purchase #2 $108.57   8.459%   $117.7539   $117.75   $117.75   $117.80  
  Purchase #3 $83.90   6.768%   $89.5784   $89.58   $89.60   $89.60  
  Purchase #4 $162.65   3.625%   $168.5461   $168.55   $168.55   $168.50  
  Purchase #5 $165.61   5.162%   $174.1588   $174.16   $174.15   $174.20  
  Purchase #6 $13.28   5.703%   $14.0374   $14.04   $14.05   $14.00  
  Purchase #7 $250.69   5.255%   $263.8638   $263.86   $263.85   $263.90  
  7 purchase totals = $854.68       $904.5756   $904.58   $904.60   $904.60