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 $119.48   3.716%   $123.9199   $123.92   $123.90   $123.90  
  Purchase #2 $10.77   6.344%   $11.4532   $11.45   $11.45   $11.50  
  Purchase #3 $140.90   8.501%   $152.8779   $152.88   $152.90   $152.90  
  Purchase #4 $243.37   6.324%   $258.7607   $258.76   $258.75   $258.80  
  Purchase #5 $124.76   10.804%   $138.2391   $138.24   $138.25   $138.20  
  Purchase #6 $62.92   10.488%   $69.519   $69.52   $69.50   $69.50  
  Purchase #7 $221.95   9.367%   $242.7401   $242.74   $242.75   $242.70  
  7 purchase totals = $924.15       $997.5099   $997.51   $997.50   $997.50