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 $52.54   13.535%   $59.6513   $59.65   $59.65   $59.70  
  Purchase #2 $41.31   7.396%   $44.3653   $44.37   $44.35   $44.40  
  Purchase #3 $227.25   4.639%   $237.7921   $237.79   $237.80   $237.80  
  Purchase #4 $113.53   5.278%   $119.5221   $119.52   $119.50   $119.50  
  Purchase #5 $34.90   11.359%   $38.8643   $38.86   $38.85   $38.90  
  Purchase #6 $174.68   4.736%   $182.9528   $182.95   $182.95   $183.00  
  Purchase #7 $219.76   6.130%   $233.2313   $233.23   $233.25   $233.20  
  7 purchase totals = $863.97       $916.3792   $916.37   $916.35   $916.50