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 $102.50   7.162%   $109.8411   $109.84   $109.85   $109.80  
  Purchase #2 $14.57   4.677%   $15.2514   $15.25   $15.25   $15.30  
  Purchase #3 $44.78   11.514%   $49.936   $49.94   $49.95   $49.90  
  Purchase #4 $222.81   5.741%   $235.6015   $235.60   $235.60   $235.60  
  Purchase #5 $182.52   8.353%   $197.7659   $197.77   $197.75   $197.80  
  Purchase #6 $130.58   8.465%   $141.6336   $141.63   $141.65   $141.60  
  Purchase #7 $85.85   5.285%   $90.3872   $90.39   $90.40   $90.40  
  7 purchase totals = $783.61       $840.4167   $840.42   $840.45   $840.40