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 $119.28   6.716%   $127.2908   $127.29   $127.30   $127.30  
  Purchase #2 $179.62   7.387%   $192.8885   $192.89   $192.90   $192.90  
  Purchase #3 $234.67   10.565%   $259.4629   $259.46   $259.45   $259.50  
  Purchase #4 $231.78   7.300%   $248.6999   $248.70   $248.70   $248.70  
  Purchase #5 $86.87   6.404%   $92.4332   $92.43   $92.45   $92.40  
  Purchase #6 $195.80   12.164%   $219.6171   $219.62   $219.60   $219.60  
  Purchase #7 $124.99   8.544%   $135.6691   $135.67   $135.65   $135.70  
  7 purchase totals = $1,173.01       $1,276.0615   $1,276.06   $1,276.05   $1,276.10