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 $78.25   10.483%   $86.4529   $86.45   $86.45   $86.50  
  Purchase #2 $46.38   13.723%   $52.7447   $52.74   $52.75   $52.70  
  Purchase #3 $236.78   3.302%   $244.5985   $244.60   $244.60   $244.60  
  Purchase #4 $94.81   5.236%   $99.7743   $99.77   $99.75   $99.80  
  Purchase #5 $235.85   10.382%   $260.3359   $260.34   $260.35   $260.30  
  Purchase #6 $64.42   12.420%   $72.421   $72.42   $72.40   $72.40  
  Purchase #7 $119.44   12.831%   $134.7653   $134.77   $134.75   $134.80  
  7 purchase totals = $875.93       $951.0926   $951.09   $951.05   $951.10