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 $76.27   10.545%   $84.3127   $84.31   $84.30   $84.30  
  Purchase #2 $244.78   6.157%   $259.8511   $259.85   $259.85   $259.90  
  Purchase #3 $15.63   10.506%   $17.2721   $17.27   $17.25   $17.30  
  Purchase #4 $194.48   7.137%   $208.36   $208.36   $208.35   $208.40  
  Purchase #5 $231.31   6.552%   $246.4654   $246.47   $246.45   $246.50  
  Purchase #6 $97.58   3.348%   $100.847   $100.85   $100.85   $100.80  
  Purchase #7 $12.84   3.440%   $13.2817   $13.28   $13.30   $13.30  
  7 purchase totals = $872.89       $930.3900   $930.39   $930.35   $930.50