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 $229.87   10.339%   $253.6363   $253.64   $253.65   $253.60  
  Purchase #2 $60.76   13.526%   $68.9784   $68.98   $69.00   $69.00  
  Purchase #3 $28.28   12.521%   $31.8209   $31.82   $31.80   $31.80  
  Purchase #4 $107.82   12.203%   $120.9773   $120.98   $121.00   $121.00  
  Purchase #5 $182.25   6.138%   $193.4365   $193.44   $193.45   $193.40  
  Purchase #6 $84.42   4.869%   $88.5304   $88.53   $88.55   $88.50  
  Purchase #7 $176.83   8.746%   $192.2956   $192.30   $192.30   $192.30  
  7 purchase totals = $870.23       $949.6754   $949.69   $949.75   $949.60