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 $24.33   5.826%   $25.7475   $25.75   $25.75   $25.70  
  Purchase #2 $232.58   7.774%   $250.6608   $250.66   $250.65   $250.70  
  Purchase #3 $20.96   9.636%   $22.9797   $22.98   $23.00   $23.00  
  Purchase #4 $25.59   11.351%   $28.4947   $28.49   $28.50   $28.50  
  Purchase #5 $111.78   7.266%   $119.9019   $119.90   $119.90   $119.90  
  Purchase #6 $250.50   4.685%   $262.2359   $262.24   $262.25   $262.20  
  Purchase #7 $55.36   4.638%   $57.9276   $57.93   $57.95   $57.90  
  7 purchase totals = $721.10       $767.9481   $767.95   $768.00   $767.90