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 $32.81   5.534%   $34.6257   $34.63   $34.65   $34.60  
  Purchase #2 $225.79   8.598%   $245.2034   $245.20   $245.20   $245.20  
  Purchase #3 $76.86   12.869%   $86.7511   $86.75   $86.75   $86.80  
  Purchase #4 $62.35   13.587%   $70.8215   $70.82   $70.80   $70.80  
  Purchase #5 $110.65   3.234%   $114.2284   $114.23   $114.25   $114.20  
  Purchase #6 $37.62   12.621%   $42.368   $42.37   $42.35   $42.40  
  Purchase #7 $218.50   13.359%   $247.6894   $247.69   $247.70   $247.70  
  7 purchase totals = $764.58       $841.6875   $841.69   $841.70   $841.70