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 $73.82   4.656%   $77.2571   $77.26   $77.25   $77.30  
  Purchase #2 $116.92   8.562%   $126.9307   $126.93   $126.95   $126.90  
  Purchase #3 $75.45   7.541%   $81.1397   $81.14   $81.15   $81.10  
  Purchase #4 $242.66   3.434%   $250.9929   $250.99   $251.00   $251.00  
  Purchase #5 $130.51   11.593%   $145.64   $145.64   $145.65   $145.60  
  Purchase #6 $119.71   6.274%   $127.2206   $127.22   $127.20   $127.20  
  Purchase #7 $122.28   7.242%   $131.1355   $131.14   $131.15   $131.10  
  7 purchase totals = $881.35       $940.3165   $940.32   $940.35   $940.20