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 $43.78   13.398%   $49.6456   $49.65   $49.65   $49.60  
  Purchase #2 $126.37   13.477%   $143.4009   $143.40   $143.40   $143.40  
  Purchase #3 $156.32   13.666%   $177.6827   $177.68   $177.70   $177.70  
  Purchase #4 $224.78   9.202%   $245.4643   $245.46   $245.45   $245.50  
  Purchase #5 $25.57   9.175%   $27.916   $27.92   $27.90   $27.90  
  Purchase #6 $170.44   10.123%   $187.6936   $187.69   $187.70   $187.70  
  Purchase #7 $235.69   12.491%   $265.13   $265.13   $265.15   $265.10  
  7 purchase totals = $982.95       $1,096.9331   $1,096.93   $1,096.95   $1,096.90