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 $41.79   12.127%   $46.8579   $46.86   $46.85   $46.90  
  Purchase #2 $30.95   13.441%   $35.11   $35.11   $35.10   $35.10  
  Purchase #3 $146.99   3.293%   $151.8304   $151.83   $151.85   $151.80  
  Purchase #4 $237.33   11.705%   $265.1095   $265.11   $265.10   $265.10  
  Purchase #5 $41.30   3.230%   $42.634   $42.63   $42.65   $42.60  
  Purchase #6 $161.55   7.598%   $173.8246   $173.82   $173.80   $173.80  
  Purchase #7 $210.76   12.253%   $236.5844   $236.58   $236.60   $236.60  
  7 purchase totals = $870.67       $951.9508   $951.94   $951.95   $951.90