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 $50.39   8.339%   $54.592   $54.59   $54.60   $54.60  
  Purchase #2 $147.82   5.403%   $155.8067   $155.81   $155.80   $155.80  
  Purchase #3 $51.47   13.849%   $58.5981   $58.60   $58.60   $58.60  
  Purchase #4 $233.32   8.461%   $253.0612   $253.06   $253.05   $253.10  
  Purchase #5 $68.35   3.408%   $70.6794   $70.68   $70.70   $70.70  
  Purchase #6 $141.78   13.638%   $161.116   $161.12   $161.10   $161.10  
  Purchase #7 $164.43   11.169%   $182.7952   $182.80   $182.80   $182.80  
  7 purchase totals = $857.56       $936.6486   $936.66   $936.65   $936.70