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 $226.65   11.843%   $253.4922   $253.49   $253.50   $253.50  
  Purchase #2 $60.86   8.378%   $65.9589   $65.96   $65.95   $66.00  
  Purchase #3 $101.61   10.715%   $112.4975   $112.50   $112.50   $112.50  
  Purchase #4 $248.27   4.105%   $258.4615   $258.46   $258.45   $258.50  
  Purchase #5 $109.97   9.402%   $120.3094   $120.31   $120.30   $120.30  
  Purchase #6 $178.46   6.613%   $190.2616   $190.26   $190.25   $190.30  
  Purchase #7 $9.65   4.187%   $10.054   $10.05   $10.05   $10.10  
  7 purchase totals = $935.47       $1,011.0351   $1,011.03   $1,011.00   $1,011.20