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 $103.44   6.622%   $110.2898   $110.29   $110.30   $110.30  
  Purchase #2 $232.57   10.351%   $256.6433   $256.64   $256.65   $256.60  
  Purchase #3 $40.94   11.457%   $45.6305   $45.63   $45.65   $45.60  
  Purchase #4 $68.28   7.722%   $73.5526   $73.55   $73.55   $73.60  
  Purchase #5 $79.28   8.517%   $86.0323   $86.03   $86.05   $86.00  
  Purchase #6 $47.97   9.621%   $52.5852   $52.59   $52.60   $52.60  
  Purchase #7 $126.61   4.858%   $132.7607   $132.76   $132.75   $132.80  
  7 purchase totals = $699.09       $757.4944   $757.49   $757.55   $757.50