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 $46.98   10.683%   $51.9989   $52.00   $52.00   $52.00  
  Purchase #2 $216.72   11.510%   $241.6645   $241.66   $241.65   $241.70  
  Purchase #3 $244.56   8.798%   $266.0764   $266.08   $266.10   $266.10  
  Purchase #4 $239.28   10.859%   $265.2634   $265.26   $265.25   $265.30  
  Purchase #5 $169.36   9.356%   $185.2053   $185.21   $185.20   $185.20  
  Purchase #6 $112.94   6.205%   $119.9479   $119.95   $119.95   $119.90  
  Purchase #7 $10.68   9.862%   $11.7333   $11.73   $11.75   $11.70  
  7 purchase totals = $1,040.52       $1,141.8897   $1,141.89   $1,141.90   $1,141.90