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 $76.32   12.532%   $85.8844   $85.88   $85.90   $85.90  
  Purchase #2 $63.63   5.693%   $67.2525   $67.25   $67.25   $67.30  
  Purchase #3 $240.33   11.184%   $267.2085   $267.21   $267.20   $267.20  
  Purchase #4 $41.98   3.828%   $43.587   $43.59   $43.60   $43.60  
  Purchase #5 $200.34   6.730%   $213.8229   $213.82   $213.80   $213.80  
  Purchase #6 $198.76   4.361%   $207.4279   $207.43   $207.45   $207.40  
  Purchase #7 $22.55   10.336%   $24.8808   $24.88   $24.90   $24.90  
  7 purchase totals = $843.91       $910.0640   $910.06   $910.10   $910.10