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 $113.59   11.564%   $126.7255   $126.73   $126.75   $126.70  
  Purchase #2 $15.43   8.837%   $16.7935   $16.79   $16.80   $16.80  
  Purchase #3 $117.48   3.853%   $122.0065   $122.01   $122.00   $122.00  
  Purchase #4 $221.44   4.694%   $231.8344   $231.83   $231.85   $231.80  
  Purchase #5 $222.94   13.526%   $253.0949   $253.09   $253.10   $253.10  
  Purchase #6 $45.86   8.418%   $49.7205   $49.72   $49.70   $49.70  
  Purchase #7 $221.92   11.608%   $247.6805   $247.68   $247.70   $247.70  
  7 purchase totals = $958.66       $1,047.8558   $1,047.85   $1,047.90   $1,047.80