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 $145.70   10.620%   $161.1733   $161.17   $161.15   $161.20  
  Purchase #2 $237.46   13.681%   $269.9469   $269.95   $269.95   $269.90  
  Purchase #3 $186.74   5.825%   $197.6176   $197.62   $197.60   $197.60  
  Purchase #4 $119.26   9.677%   $130.8008   $130.80   $130.80   $130.80  
  Purchase #5 $13.38   12.813%   $15.0944   $15.09   $15.10   $15.10  
  Purchase #6 $169.52   4.621%   $177.3535   $177.35   $177.35   $177.40  
  Purchase #7 $213.29   13.312%   $241.6832   $241.68   $241.70   $241.70  
  7 purchase totals = $1,085.35       $1,193.6697   $1,193.66   $1,193.65   $1,193.70