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 $192.30   13.229%   $217.7394   $217.74   $217.75   $217.70  
  Purchase #2 $68.54   11.491%   $76.4159   $76.42   $76.40   $76.40  
  Purchase #3 $60.41   4.785%   $63.3006   $63.30   $63.30   $63.30  
  Purchase #4 $169.37   6.616%   $180.5755   $180.58   $180.60   $180.60  
  Purchase #5 $6.98   11.667%   $7.7944   $7.79   $7.80   $7.80  
  Purchase #6 $111.30   7.253%   $119.3726   $119.37   $119.35   $119.40  
  Purchase #7 $236.99   9.462%   $259.414   $259.41   $259.40   $259.40  
  7 purchase totals = $845.89       $924.6124   $924.61   $924.60   $924.60