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 $82.68   3.661%   $85.7069   $85.71   $85.70   $85.70  
  Purchase #2 $127.48   4.803%   $133.6029   $133.60   $133.60   $133.60  
  Purchase #3 $239.53   4.334%   $249.9112   $249.91   $249.90   $249.90  
  Purchase #4 $204.64   6.162%   $217.2499   $217.25   $217.25   $217.20  
  Purchase #5 $124.36   10.133%   $136.9614   $136.96   $136.95   $137.00  
  Purchase #6 $162.83   7.677%   $175.3305   $175.33   $175.35   $175.30  
  Purchase #7 $13.33   3.150%   $13.7499   $13.75   $13.75   $13.70  
  7 purchase totals = $954.85       $1,012.5127   $1,012.51   $1,012.50   $1,012.40