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 $66.88   10.223%   $73.7171   $73.72   $73.70   $73.70  
  Purchase #2 $191.49   9.118%   $208.9501   $208.95   $208.95   $209.00  
  Purchase #3 $155.35   6.389%   $165.2753   $165.28   $165.30   $165.30  
  Purchase #4 $196.41   12.117%   $220.209   $220.21   $220.20   $220.20  
  Purchase #5 $14.72   8.605%   $15.9867   $15.99   $16.00   $16.00  
  Purchase #6 $63.95   9.768%   $70.1966   $70.20   $70.20   $70.20  
  Purchase #7 $46.47   5.277%   $48.9222   $48.92   $48.90   $48.90  
  7 purchase totals = $735.27       $803.2570   $803.27   $803.25   $803.30