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 $242.38   11.150%   $269.4054   $269.41   $269.40   $269.40  
  Purchase #2 $233.69   5.679%   $246.9613   $246.96   $246.95   $247.00  
  Purchase #3 $229.42   3.630%   $237.7479   $237.75   $237.75   $237.70  
  Purchase #4 $133.73   8.347%   $144.8924   $144.89   $144.90   $144.90  
  Purchase #5 $58.84   11.565%   $65.6448   $65.64   $65.65   $65.60  
  Purchase #6 $177.66   10.492%   $196.3001   $196.30   $196.30   $196.30  
  Purchase #7 $51.94   5.437%   $54.764   $54.76   $54.75   $54.80  
  7 purchase totals = $1,127.66       $1,215.7159   $1,215.71   $1,215.70   $1,215.70