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 $41.49   13.171%   $46.9546   $46.95   $46.95   $47.00  
  Purchase #2 $19.42   8.669%   $21.1035   $21.10   $21.10   $21.10  
  Purchase #3 $68.88   5.533%   $72.6911   $72.69   $72.70   $72.70  
  Purchase #4 $117.80   3.516%   $121.9418   $121.94   $121.95   $121.90  
  Purchase #5 $181.72   10.285%   $200.4099   $200.41   $200.40   $200.40  
  Purchase #6 $236.92   9.246%   $258.8256   $258.83   $258.85   $258.80  
  Purchase #7 $213.77   10.205%   $235.5852   $235.59   $235.60   $235.60  
  7 purchase totals = $880.00       $957.5117   $957.51   $957.55   $957.50