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 $239.92   4.573%   $250.8915   $250.89   $250.90   $250.90  
  Purchase #2 $111.31   9.119%   $121.4604   $121.46   $121.45   $121.50  
  Purchase #3 $58.95   3.865%   $61.2284   $61.23   $61.25   $61.20  
  Purchase #4 $87.63   5.739%   $92.6591   $92.66   $92.65   $92.70  
  Purchase #5 $25.26   4.276%   $26.3401   $26.34   $26.35   $26.30  
  Purchase #6 $243.29   5.482%   $256.6272   $256.63   $256.65   $256.60  
  Purchase #7 $226.55   11.528%   $252.6667   $252.67   $252.65   $252.70  
  7 purchase totals = $992.91       $1,061.8734   $1,061.88   $1,061.90   $1,061.90