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 $247.27   10.478%   $273.179   $273.18   $273.20   $273.20  
  Purchase #2 $129.43   3.278%   $133.6727   $133.67   $133.65   $133.70  
  Purchase #3 $159.58   11.536%   $177.9891   $177.99   $178.00   $178.00  
  Purchase #4 $167.79   5.411%   $176.8691   $176.87   $176.85   $176.90  
  Purchase #5 $38.73   11.250%   $43.0871   $43.09   $43.10   $43.10  
  Purchase #6 $179.31   3.673%   $185.8961   $185.90   $185.90   $185.90  
  Purchase #7 $229.54   5.849%   $242.9658   $242.97   $242.95   $243.00  
  7 purchase totals = $1,151.65       $1,233.6589   $1,233.67   $1,233.65   $1,233.80