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 $46.51   6.610%   $49.5843   $49.58   $49.60   $49.60  
  Purchase #2 $250.84   4.861%   $263.0333   $263.03   $263.05   $263.00  
  Purchase #3 $50.47   3.545%   $52.2592   $52.26   $52.25   $52.30  
  Purchase #4 $246.81   9.714%   $270.7851   $270.79   $270.80   $270.80  
  Purchase #5 $187.60   12.149%   $210.3915   $210.39   $210.40   $210.40  
  Purchase #6 $70.42   4.739%   $73.7572   $73.76   $73.75   $73.80  
  Purchase #7 $194.71   11.360%   $216.8291   $216.83   $216.85   $216.80  
  7 purchase totals = $1,047.36       $1,136.6397   $1,136.64   $1,136.70   $1,136.70