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 $69.43   13.262%   $78.6378   $78.64   $78.65   $78.60  
  Purchase #2 $22.89   6.275%   $24.3263   $24.33   $24.35   $24.30  
  Purchase #3 $41.94   11.408%   $46.7245   $46.72   $46.70   $46.70  
  Purchase #4 $209.29   8.595%   $227.2785   $227.28   $227.30   $227.30  
  Purchase #5 $214.93   5.396%   $226.5276   $226.53   $226.55   $226.50  
  Purchase #6 $195.78   5.350%   $206.2542   $206.25   $206.25   $206.30  
  Purchase #7 $233.78   8.793%   $254.3363   $254.34   $254.35   $254.30  
  7 purchase totals = $988.04       $1,064.0852   $1,064.09   $1,064.15   $1,064.00