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 $77.41   6.368%   $82.3395   $82.34   $82.35   $82.30  
  Purchase #2 $246.99   11.425%   $275.2086   $275.21   $275.20   $275.20  
  Purchase #3 $185.68   4.426%   $193.8982   $193.90   $193.90   $193.90  
  Purchase #4 $203.26   11.815%   $227.2752   $227.28   $227.30   $227.30  
  Purchase #5 $90.70   11.597%   $101.2185   $101.22   $101.20   $101.20  
  Purchase #6 $88.38   9.801%   $97.0421   $97.04   $97.05   $97.00  
  Purchase #7 $73.26   4.763%   $76.7494   $76.75   $76.75   $76.70  
  7 purchase totals = $965.68       $1,053.7315   $1,053.74   $1,053.75   $1,053.60