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 $216.31   10.804%   $239.6801   $239.68   $239.70   $239.70  
  Purchase #2 $121.86   7.207%   $130.6425   $130.64   $130.65   $130.60  
  Purchase #3 $158.80   9.283%   $173.5414   $173.54   $173.55   $173.50  
  Purchase #4 $62.30   7.400%   $66.9102   $66.91   $66.90   $66.90  
  Purchase #5 $131.93   7.657%   $142.0319   $142.03   $142.05   $142.00  
  Purchase #6 $78.44   4.515%   $81.9816   $81.98   $82.00   $82.00  
  Purchase #7 $207.50   8.331%   $224.7868   $224.79   $224.80   $224.80  
  7 purchase totals = $977.14       $1,059.5745   $1,059.57   $1,059.65   $1,059.50