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 $87.46   10.441%   $96.5917   $96.59   $96.60   $96.60  
  Purchase #2 $223.69   4.462%   $233.671   $233.67   $233.65   $233.70  
  Purchase #3 $118.69   5.454%   $125.1634   $125.16   $125.15   $125.20  
  Purchase #4 $133.39   4.867%   $139.8821   $139.88   $139.90   $139.90  
  Purchase #5 $162.54   3.286%   $167.8811   $167.88   $167.90   $167.90  
  Purchase #6 $49.54   6.322%   $52.6719   $52.67   $52.65   $52.70  
  Purchase #7 $42.60   3.612%   $44.1387   $44.14   $44.15   $44.10  
  7 purchase totals = $817.91       $859.9999   $859.99   $860.00   $860.10