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 $246.69   10.826%   $273.3967   $273.40   $273.40   $273.40  
  Purchase #2 $57.41   8.452%   $62.2623   $62.26   $62.25   $62.30  
  Purchase #3 $213.43   10.781%   $236.4399   $236.44   $236.45   $236.40  
  Purchase #4 $214.66   9.579%   $235.2223   $235.22   $235.20   $235.20  
  Purchase #5 $228.89   10.640%   $253.2439   $253.24   $253.25   $253.20  
  Purchase #6 $226.83   5.603%   $239.5393   $239.54   $239.55   $239.50  
  Purchase #7 $222.68   5.384%   $234.6691   $234.67   $234.65   $234.70  
  7 purchase totals = $1,410.59       $1,534.7735   $1,534.77   $1,534.75   $1,534.70