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 $243.99   10.376%   $269.3064   $269.31   $269.30   $269.30  
  Purchase #2 $199.72   8.254%   $216.2049   $216.20   $216.20   $216.20  
  Purchase #3 $132.48   10.380%   $146.2314   $146.23   $146.25   $146.20  
  Purchase #4 $163.32   7.695%   $175.8875   $175.89   $175.90   $175.90  
  Purchase #5 $126.93   9.727%   $139.2765   $139.28   $139.30   $139.30  
  Purchase #6 $209.40   9.151%   $228.5622   $228.56   $228.55   $228.60  
  Purchase #7 $65.29   11.765%   $72.9714   $72.97   $72.95   $73.00  
  7 purchase totals = $1,141.13       $1,248.4403   $1,248.44   $1,248.45   $1,248.50