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 $144.63   10.301%   $159.5283   $159.53   $159.55   $159.50  
  Purchase #2 $53.34   9.450%   $58.3806   $58.38   $58.40   $58.40  
  Purchase #3 $136.48   11.320%   $151.9295   $151.93   $151.95   $151.90  
  Purchase #4 $107.51   10.616%   $118.9233   $118.92   $118.90   $118.90  
  Purchase #5 $203.78   8.809%   $221.731   $221.73   $221.75   $221.70  
  Purchase #6 $78.99   11.466%   $88.047   $88.05   $88.05   $88.00  
  Purchase #7 $204.81   10.214%   $225.7293   $225.73   $225.75   $225.70  
  7 purchase totals = $929.54       $1,024.2690   $1,024.27   $1,024.35   $1,024.10