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 $71.42   8.522%   $77.5064   $77.51   $77.50   $77.50  
  Purchase #2 $222.87   5.753%   $235.6917   $235.69   $235.70   $235.70  
  Purchase #3 $89.70   5.580%   $94.7053   $94.71   $94.70   $94.70  
  Purchase #4 $130.93   3.601%   $135.6448   $135.64   $135.65   $135.60  
  Purchase #5 $181.54   10.670%   $200.9103   $200.91   $200.90   $200.90  
  Purchase #6 $70.61   7.658%   $76.0173   $76.02   $76.00   $76.00  
  Purchase #7 $169.65   13.596%   $192.7156   $192.72   $192.70   $192.70  
  7 purchase totals = $936.72       $1,013.1914   $1,013.20   $1,013.15   $1,013.10