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 $47.63   10.601%   $52.6793   $52.68   $52.70   $52.70  
  Purchase #2 $239.54   11.761%   $267.7123   $267.71   $267.70   $267.70  
  Purchase #3 $68.41   12.599%   $77.029   $77.03   $77.05   $77.00  
  Purchase #4 $213.61   4.265%   $222.7205   $222.72   $222.70   $222.70  
  Purchase #5 $45.94   5.351%   $48.3982   $48.40   $48.40   $48.40  
  Purchase #6 $115.67   6.388%   $123.059   $123.06   $123.05   $123.10  
  Purchase #7 $136.60   9.109%   $149.0429   $149.04   $149.05   $149.00  
  7 purchase totals = $867.40       $940.6412   $940.64   $940.65   $940.60